JUSTICE RATHJE delivered the opinion of the court:
The State appeals from an order of the appellate court holding that respondent, G.O., is entitled to a jury trial and that respondent's confession was involuntary. See 304 Ill. App. 3d 719. We vacate the appellate court's holding that respondent is entitled to a jury trial and reverse the holding that respondent's confession was involuntary.
The State, relying upon a theory of accountability, filed a petition in the circuit court of Cook County to adjudicate respondent delinquent for the first degree murder (720 ILCS 5/9-1(a)(1), (a)(2) (West 1998)) of Rafael Kubera. Respondent also faced related allegations of aggravated discharge of a firearm (720 ILCS 5/24-1.2(a)(2) (West 1998)), aggravated battery (720 ILCS 5/12-4(a) (West 1998)), and aggravated battery with a firearm (720 ILCS 5/12-4.2(a)(1) (West 1998)). Respondent requested a jury trial. The trial court denied respondent's request. Respondent also sought to suppress incriminating statements that he had made. After a hearing, the trial court denied this motion.
Subsequently, the trial court adjudicated respondent delinquent on all charges. Pursuant to section 5-33(1.5) of the Juvenile Court Act of 1987 (705 ILCS 405/5-33(1.5) (West 1996) (now 705 ILCS 405/5-750(2) (West 1998))), the trial court declared respondent a ward of the court and ordered him committed to the Department of Corrections, Juvenile Division, until his "21st birthday, without the possibility of parole, furlough, or non-emergency authorized absence for a period of 5 years." See 705 ILCS 405/5-33(1.5) (West 1996). Respondent timely appealed.
The appellate court held that the trial court denied respondent his right to equal protection as guaranteed by the federal and state constitutions (see U.S. Const., amend. XIV; Ill. Const. 1970, art. I, §2) when it denied his request for a jury trial. The court explained that the sentence to which respondent was subject was similar to the sentences imposed upon habitual and violent juvenile offenders. *fn1 Compare 705 ILCS 405/5-33(1.5) (West 1996) with 705 ILCS 405/5-35(f) (West 1996) (now 705 ILCS 405/5-815(f) (West 1998)) (requiring a habitual juvenile offender to be committed to the Department of Corrections, Juvenile Division, "until his 21st birthday, without possibility of parole, furlough, or non-emergency authorized absence") and 705 ILCS 405/5-36(f) (West 1996) (now 705 ILCS 405/5-820(f) (West 1998)) (requiring a violent juvenile offender to be committed to the Department of Corrections, Juvenile Division, "until his or her 21st birthday, without possibility of parole, furlough, or non-emergency authorized absence"). The court described all three sentences as "punitive, determinate, non-discretionary sentences of commitment to the age of 21 without hope of parole or furlough for at least five years from the date of commitment." 304 Ill. App. 3d at 727. The court reasoned that the similar sentences rendered respondent similarly situated to habitual and violent juvenile offenders. Notwithstanding the fact that the three are similarly situated, the Juvenile Court Act treats juveniles charged with first degree murder differently than it treats juvenile offenders and violent juvenile offenders. Specifically, the Juvenile Court Act grants a jury trial to both habitual and violent juvenile offenders, but it does not grant such a right to juveniles charged with first degree murder. See 705 ILCS 405/5-35(d), 5-36(d) (West 1996). The appellate court concluded that no rational basis existed for granting a jury trial to habitual and violent juvenile offenders while denying one to juveniles charged with first degree murder. 304 Ill. App. 3d at 727-29.
The appellate court also examined the evidence that had been presented at the suppression hearing and concluded that the trial court erred in denying respondent's motion to suppress. Subsequently, the State sought leave to appeal, both as a matter of right and as a matter of discretion (see 177 Ill. 2d R. 315; 134 Ill. 2d R. 317). *fn2 We granted the State's petition and ordered that the action be considered on an expedited basis. We also granted the motions of the Cook County public defender and the Children and Family Justice Center to file briefs as amici curiae.
We address first the State's argument that the appellate court erred in concluding that the trial court's refusal to grant respondent a jury trial denied him the equal protection of the laws. The basis for the appellate court's opinion is the similar sentences imposed on juveniles adjudicated delinquent of first degree murder and those imposed on juveniles adjudicated delinquent as habitual and violent juvenile offenders. See 304 Ill. App. 3d at 727.
The sentencing provision for juveniles charged with first degree murder is found at section 5-33(1.5). This section was enacted as part of Public Act 88-680 (Pub. Act 88-680, eff. January 1, 1995), commonly known as the Safe Neighborhoods Law. In People v. Cervantes, 189 Ill. 2d 80 (1999), this court held that the General Assembly violated the single subject clause of the Illinois Constitution (Ill. Const. 1970, art. IV, §8(d)) when it enacted Public Act 88-680. When an act is held unconstitutional in its entirety, it is void ab initio; the state of the law is as if the act had never been passed. People v. Tellez-Valencia, 188 Ill. 2d 523, 525 (1999); see also People v. Gersch, 135 Ill. 2d 384, 390 (1990). Thus, respondent is no longer subject to a mandatory sentencing requirement. Instead, he is now treated similarly to all juvenile offenders except habitual and violent juvenile offenders. Because respondent is unquestionably not similarly situated to habitual and violent juvenile offenders, we have no basis upon which to conclude that the trial court's denial of respondent's request for a jury trial denied respondent of the equal protection of the law.
Respondent argues that, even if he is not entitled to a jury trial as a matter of equal protection, both the federal and state constitutions guarantee him such a right both as a matter of due process and as a matter of the constitutionally guaranteed right to a jury trial. See U.S. Const., amends. VI, XIV, Ill. Const. 1970, art. I, §§2, 8. Both this court and the Supreme Court have previously rejected such arguments. See McKeiver v. Pennsylvania, 403 U.S. 528, 29 L. Ed. 2d 647, 91 S. Ct. 1976 (1971); People ex rel. Carey v. Chrastka, 83 Ill. 2d 67 (1980); In re Fucini, 44 Ill. 2d 305 (1970). Respondent urges us to reconsider these decisions in light of the fact that the mandatory minimum sentence required by section 5-33(1.5) renders the process to which respondent is subject much more punitive than rehabilitative. Here, however, respondent is no longer subject to the mandatory minimum sentence, and respondent has given us no other reason to re-examine our earlier decisions. *fn3 Consequently, we must reject respondent's argument.
Because the law underlying the appellate court's judgment has now been rendered void, we must vacate the appellate court's judgment holding that respondent was denied his equal protection rights when the trial court denied his request for a new trial.
Respondent's Motion to Cite Supplemental Authority and the State's Reply Brief to the Briefs of the Amici Curiae
After this court issued its opinion in Cervantes, respondent sought leave to cite Cervantes as additional authority. In section II of this motion, respondent asserts that the legislature has reenacted the mandatory sentencing provision for juveniles charged with first degree murder (see 705 ILCS 405/5-750(2) (West 1998)). Respondent contends that, because this provision has been reenacted, this court should, because of the "great public interest," decide whether a juvenile charged with first degree murder is entitled to a jury trial.
Similarly, the State, in its reply brief to the briefs of the amici curiae, devotes approximately a third of its brief to discussing the effect of Cervantes. The State argues that (1) because of the reenactment of the sentencing provision, we should address whether juveniles charged with first degree murder are entitled to a jury trial; and (2) respondent is subject to the reenacted sentencing provision even though it was not effective until after the events forming the foundation of the finding of delinquency occurred. Subsequently, respondent moved to strike the State's reply brief. We ordered that motion taken with the case.
This court's rules governing appeals provide, "The reply brief, if any, shall be confined strictly to replying to arguments presented in the brief of the appellee ***." (Emphasis added.) 177 Ill. 2d R. 341(g). The first third of the State's reply brief addresses issues contained within neither respondent's brief nor the briefs of the amici curiae, which were filed in support of the respondent's position. Because argument I of the State's brief violates Rule 341(g), we grant respondent's motion in part and strike argument I of the State's brief. In so doing, we note that if the State wished to brief these issues, it should have sought leave from this court to do so.
We turn now to respondent's argument. Respondent concedes that he is no longer subject to the mandatory sentencing requirements. He argues, however, that this court should issue what would in effect be an advisory opinion deciding whether, under the reenacted version of the sentencing provision for juveniles found delinquent of first degree murder, juveniles are entitled to a jury trial. Aside from the question of whether respondent should have raised this issue earlier, *fn4 we note that respondent's argument contains no citation to any authority that would permit this court to issue such an advisory opinion. Because respondent has failed to cite any authority to support his argument, we find it waived. See 177 Ill. 2d R. 341(e)(7); People v. Franklin, 167 Ill. 2d 1, 20 (1995).
Voluntariness of Respondent's Confession
We turn now to whether defendant's confession was voluntary. Before addressing the merits of this issue, we must first determine the proper standard of review. The State argues that we cannot reverse the trial court's ruling denying defendant's motion to suppress unless the court's conclusion is against the manifest weight of the evidence. The appellate court, finding that neither the facts nor the credibility of the witnesses was at issue, reviewed the trial court's ruling de novo. See 304 Ill. App. 3d at 730. Respondent argues that, regardless of which standard of review is applied, the trial court erred in denying respondent's motion to suppress. Nevertheless, respondent contends that de novo review is appropriate because "[o]nly the State's witnesses presented evidence with respect to the alleged statements and the immediate surrounding circumstances."
Traditionally, this court has held that, when an appellate court reviews a trial court's ruling on a defendant's motion to suppress involuntary statements, the appellate court should affirm the trial court's judgment unless the judgment was manifestly erroneous. See People v. Oaks, 169 Ill. 2d 409, 447 (1996) ("this court has never departed from the `manifestly erroneous' standard in reviewing the denial of a defendant's motion to suppress based upon the voluntariness of a confession"). In Oaks, however, this court reviewed the ruling de novo because the record contained both a videotape and a transcript of the interrogation. Oaks, 169 Ill. 2d at 447.
After this court decided Oaks, the Supreme Court held that, when an appellate court reviews rulings on a motion to suppress involving questions of probable cause and reasonable suspicion, the reviewing court should review de novo the findings with respect to probable cause and reasonable suspicion. Ornelas v. United States, 517 U.S. 690, 699, 134 L. Ed. 2d 911, 920, 116 S. Ct. 1657, 1663 (1996). The Court explained that de novo review was justified for three reasons. First, "independent appellate review of these ultimate determinations of reasonable suspicion and probable cause is consistent with the position we have taken in past cases." Ornelas, 517 U.S. at 697, 134 L. Ed. 2d at 919, 116 S. Ct. at 1662. Second, "the legal rules for probable cause and reasonable suspicion acquire content only through application. Independent review is therefore necessary if appellate courts are to maintain control of, and to clarify, the legal principles." Ornelas, 517 U.S. at 697, 134 L. Ed. 2d at 919, 116 S. Ct. at 1662. Third, "de novo review tends to unify precedent and will come closer to providing law enforcement officers with a defined `set of rules which, in most instances, makes it possible to reach a correct determination beforehand as to whether an invasion of privacy is justified in the interest of law enforcement.' " Ornelas, 517 U.S. at 698, 134 L. Ed. 2d at 919, 116 S. Ct. at 1662, quoting New York v. Belton, 453 U.S. 454, 458, 69 L. Ed. 2d 768, 773, 101 S. Ct. 2860, 2863 (1981). The Court cautioned, however, that findings of historical fact should be reviewed only for clear error and that reviewing courts must give due weight to inferences drawn from those facts by the fact finder. Ornelas, 517 U.S. at 699, 134 L. Ed. 2d at 920, 116 S. Ct. at 1663.
Thereafter, the United States Court of Appeals, Seventh Circuit, held that "Ornelas requires that the ultimate question of whether a confession is voluntary is a matter of law that must be reviewed de novo." United States v. D.F., 115 F.3d 413, 419 (7th Cir. 1996). In reaching this conclusion, the court noted that the same factors that the Supreme Court found dispositive in Ornelas apply equally to questions of voluntariness. First, the Supreme Court has traditionally treated the question of the voluntariness of a confession as a question of law. D.F., 115 F.3d at 418, citing Arizona v. Fulminante, 499 U.S. 279, 113 L. Ed. 2d 302, 111 S. Ct. 1246 (1991); Miller v. Fenton, 474 U.S. 104, 110, 88 L. Ed. 2d 405, 411, 106 S. Ct. 445, 449 (1985); see also Haynes v. Washington, 373 U.S. 503, 515-16, 10 L. Ed. 2d 513, 522, 83 S. Ct. 1336, 1344 (1963). Second, the term voluntariness "is certainly given content through case-by-case adjudication, an adjudication tempered by the discipline of traditional common-law methodology. When employed as a constitutional standard of adjudication, it presents a very definite need for uniformity of meaning and consistency of application." D.F., 115 F.3d at 417. Third, the court explained that the question of whether a confession is voluntary " `turns as much on whether the techniques for extracting the statements, as applied to this suspect, are compatible with a system that presumes innocence and assures that a conviction will not be secured by inquisitorial means as on whether the defendant's will was in fact overborne.' " (Emphasis omitted.) D.F., 115 F.3d at 418, quoting Miller, 474 U.S. at 116, 88 L. Ed. 2d at 414-15, 106 S. Ct. at 452-53. Given this, the "unification of precedent by appellate courts is especially important because it comes closer to providing law enforcement officers with a set of rules upon which they can act with the assurance that they are not going beyond the pale of the Constitution." D.F., 115 F.3d at 417. Because the factors used in Ornelas apply equally to questions of the voluntariness of a confession, the Seventh Circuit concluded that "Ornelas requires that the ultimate question of whether a confession is voluntary is a matter of law that must be reviewed de novo." D.F., 115 F.3d at 419. In reaching this conclusion, the court, like the Supreme Court in Ornelas, emphasized that "the determination of the historical facts of the case are the proper domain of the trial court and that our review of its findings in that regard will be for clear error." D.F., 115 F.3d at 419. Notably, virtually every other federal court of appeals agrees with this conclusion. See United States v. Tompkins, 130 F.3d 117, 120 n.10 (5th Cir. 1997) (citing cases from numerous federal appellate courts and noting that the question of whether a confession is voluntary "is uniformly held to be subject to de novo review").
After reviewing Ornelas and D.F., we agree with the Seventh Circuit that the decision in Ornelas applies equally to questions of the voluntariness of a confession and that the federal appellate courts and the Supreme Court review de novo the question of the voluntariness of a confession. The question facing us is whether we should adopt the same standard.
First, we note that this court has followed Ornelas. See People v. Wardlow, 183 Ill. 2d 306, 311 (1998), rev'd on other grounds, ____ U.S. ____, 143 L. Ed. 2d 669, 119 S. Ct. 1573 (1999). Thus, this court has already found persuasive the principles relied on in Ornelas. After considering this fact and reviewing the above cases, we believe that the same principles apply to our review of the voluntariness of a confession. A de novo standard of review ensures that our courts of review maintain and clarify the legal principals governing confessions. This, in turn, allows our reviewing courts to develop a uniform body of precedent that will enable police officers to determine, before attempting to obtain confession, what behavior is constitutionally permissible.
Consequently, in reviewing whether respondent's confession was voluntary, we will accord great deference to the trial court's factual findings, and we will reverse those findings only if they are against the manifest weight of the evidence. However, we will review de novo the ultimate question of whether the confession was voluntary. We caution that, for this standard of review to function as it is intended, trial courts must exercise their responsibility to make factual findings when ruling on motions to suppress. Reviewing courts should not be required to surmise what factual findings that the trial court made. Instead, the trial court should make clear any factual findings upon which it is relying. It is only through this synergy between the trial ...