OPINION
MANNHEIMER, Judge.Torey John Tuttle was one of a group of men who attacked another man for the purpose of stealing his money. One member of the group fired several shots at the victim, but the victim escaped unharmed. Based on this incident, seven men — including Tuttle— were indicted for first-degree robbery, AS 11.41.500(a)(1). Some of these seven defendants went to trial, but Tuttle ultimately pleaded no contest to this charge.
First-degree robbery is a class A felony.1 Because Tuttle was a first felony offender, he faced a presumptive term of either 5 years’ or 7 years’ imprisonment, depending on whether he personally possessed a firearm during the robbery.2
The evidence was in conflict on this point. According to a police report filed in this case, the victim of the robbery initially told the police that another defendant, Sean Beatty, was the one who fired the gun at him. However, when Beatty was interviewed (under the authority of a Glass warrant3), he stated *886that Tuttle was the shooter. Another participant in the robbery, Sean Roe, corroborated this version of events. Roe told the police that he initially had the gun, but then Tuttle yanked the weapon away from him, commenting that Roe “didn’t have [the] balls” to use it. Finally, another member of the group, Jerry Christopher (“J.C.”) Lee, also stated that Tuttle was the shooter — although his basis for knowing this was uncertain, since he apparently left the scene before the robbery began. Tuttle, for his part, told the police that he never possessed the gun.
Superior Court Judge Larry D. Card was the sentencing judge who was asked to resolve this disputed issue of fact. By the time of Tuttle’s sentencing hearing, Judge Card was well familiar with the case: he had already presided over the trials of two of Tuttle’s co-defendants (including Sean Roe), and he had presided over the sentencings of four of Tuttle’s co-defendants.
Judge Card resolved this factual dispute against Tuttle. That is, Judge Card found that Tuttle possessed (and fired) the gun during the robbery, and that Tuttle therefore faced a 7-year presumptive term rather than a 5-year presumptive term. However, when Judge Card made this finding, he expressly relied on the observations he made while presiding over Roe’s trial:
The Court: I sat through the trial of Mr. Roe[, and] I’m satisfied [that] Mr. Tuttle, if [he did not seize] the gun [from Roe], was handed the gun by Mr. Roe_
[When] Mr. Tuttle [was interviewed,] he denied ever having the gun or firing the gun. [But] by the process of elimination— [and] I’ve heard the trials — I find that [Tuttle] was telling Detective Vandervalk a lie. He was the one who took the gun and fired the gun....
I think that Mr. Tuttle fired at [the victim]. I think [that] Mr. Roe ... was very believable when I listened to him, when I observed him [at his trial]. [He] was very truthful. And I observed his demeanor, and I’m satisfied that Mr. Tuttle did take the gun from ... Sean Roe [and] did fire the gun....
I’m satisfied that Mr. Tuttle was the one who took the gun [from Roe] and fired the gun. And [this is proved] by a preponderance [of the evidence], which is the requirement ... in a proceeding such as this.
On appeal, Tuttle argues that Judge Card violated his right to due process when he relied on Roe’s testimony. Tuttle and his attorney were aware, before sentencing, that Roe had identified Tuttle as the shooter. But Tuttle points out that he never had the opportunity to cross-examine Roe on. this issue and point out the reasons why one might distrust Roe’s account of what happened.
The State responds that Tuttle had no right to confront Roe at the sentencing hearing. This is correct. Under Evans v. State, 23 P.3d 650, 652 (Alaska App.2001), and Hamilton v. State, 771 P.2d 1358, 1362-63 (Alaska App.1989), Judge Card could rely on Roe’s out-of-court statements unless Tuttle took the stand and offered a testimonial denial of the State’s assertion that he was the shooter. Tuttle did not do this. Thus, Judge Card could properly rely on the content of Roe’s out-of-court statements.
(We again emphasize that Tuttle does not allege that he was ignorant of Roe’s account of the robbery when he prepared for his own sentencing. Tuttle’s attorney acknowledged that he had received “all discovery” concerning Roe’s statements.)
It is possible, however, that Judge Card acted improperly when he resolved the credibility of Roe’s version of events by relying on his personal observations of Roe at trial. When a judge hears the separate trials or sentencings of two or more co-defendants, the judge is generally obliged to “set aside any judicially acquired information that [is] not admissible against [a particular] defendant, and decide [each defendant’s] case ... solely upon the evidence presented in [that defendant’s] case”.4
*887A judge can not rely on personal knowledge of matters outside the judicial record.5 Although Judge Card was entitled to rely on the content of Roe’s testimony (because Roe’s statements had been disclosed to Tuttle), one might plausibly argue that the judge violated this rule when he expressly resolved the evidentiary dispute at Tuttle’s sentencing hearing by relying on Roe’s demeanor while testifying at a separate trial — for Roe’s demeanor was something that Judge Card personally observed but which was not known to Tuttle or his attorney.
Nevertheless, we conclude (for two reasons) that we should not resolve this issue of law.
First, Tuttle has failed to adequately brief it. Tuttle’s brief focuses purely on his purported right to confront Roe — a right that he did not have — and, moreover, he cites no case law in support of his argument. We conclude that even if Tuttle might validly challenge Judge Card’s decision on the ground we have just described, that challenge has been inadequately briefed.6
Second, we must in any event vacate Judge Card’s finding. As can be seen from Judge Card’s remarks quoted above, he applied the “preponderance of the evidence” standard of proof when resolving the question of whether Tuttle possessed a firearm during the robbery. This was error. Because the applicable presumptive term hinges on this factual issue, the State must prove Tuttle’s possession of the firearm beyond a reasonable doubt. We decided this precise question in Huf v. State, 675 P.2d 268, 273-74 (Alaska App.1984).
Tuttle raises one final claim on appeal. Relying on our decision in Malloy v. State, 1 P.3d 1266 (Alaska App.2000), Tuttle argues that his possession of a firearm during the robbery was not a sentencing factor but was actually an element of the crime, and thus the State was obliged to prove this fact to a jury rather than proving it to Judge Card.
But Tuttle’s argument is rebutted by the Malloy opinion itself. In Malloy, we followed the Alaska Supreme Court’s decision in Donlun v. State7 and held that any factor which increases the maximum punishment for an offense is an element of the offense that must be proved to a jury.8 At the same time, we carefully explained that this rule did not apply to the factors that trigger the various presumptive terms specified in AS 12.55.125.9
To summarize our holding:
First, Tuttle’s possession of a firearm is not an element of the offense to be proved to the finder of fact at trial, but rather a sentencing factor to be proved to the court at sentencing.
Second, because Tuttle did not offer a testimonial denial of the State’s assertion that he possessed a firearm during the robbery, Judge Card was entitled to rely on out-of-court statements made by Tuttle’s co-defendants (and other witnesses) concerning this issue — although it is possible that he was not entitled to rely on his personal observations of Sean Roe’s demeanor.
*888Third, we vacate Judge Card’s finding that Tuttle possessed a firearm during the robbery because Judge Card applied the wrong standard of proof. The State was obliged to prove this fact beyond a reasonable doubt.
We VACATE Tuttle’s sentence, and we remand this case to the superior court. Judge Card should re-determine the question of whether Tuttle possessed a firearm during the robbery. If the judge again concludes that the State has proved the applicability of the 7-year presumptive term, he may reimpose the same sentence. However, if Judge Card concludes that the State has not proved Tuttle’s possession of a firearm beyond a reasonable doubt, he should re-sentence Tuttle using a 5-year presumptive term as the starting point.
We do not retain jurisdiction of this case.
. See AS 11.41.500(b).
. See AS 12.55.125(c)(l)-(2)(A).
. See State v. Glass, 583 P.2d 872 (Alaska 1978) (generally requiring the police to obtain a warrant before secretly monitoring or taping a conversation).
. Boyd v. State, 321 Md. 69, 581 A.2d 1, 6-7 (1990). Boyd holds that a judge's exposure to information from a co-defendant's separate trial does not require the judge's disqualification, see id. at 3-6, 9, but it also confirms a judge's duty to decide each defendant’s case on its own merits, see id. at 3-7.
. See Ex parte Rains, 555 S.W.2d 478, 480-81 (Tex.Crim.App.1977); State v. Jamison, 20 Ohio App.2d 196, 253 N.E.2d 316, 318 (1969); State v. Denoon, 8 Ohio App.2d 70, 220 N.E.2d 730, 730-31 (1966).
. See Legge v. Greig, 880 P.2d 606, 609 (Alaska 1994):
Appellate briefs should be crafted to serve their primary puiposeL] which is to bring together the relevant facts and law in a clear and concise manner so that the court is fully informed. Kiester v. Humana Hosp. of Alaska, Inc,, 843 P.2d 1219, 1227 n. 8 (Alaska 1992) (quoting Dickerson v. Geiermann, 368 P.2d 217, 218 (Alaska 1962)). An issue given only cursory treatment in a brief will be treated as abandoned. Petersen v. Mutual Life Ins. Co., 803 P.2d 406, 410 (Alaska 1990). [The appellant’s] cursory briefing of a significant and potentially difficult ... issue leaves this court virtually no informed basis for meaningful appellate review.
. 527 P.2d 472 (Alaska 1974).
. See Malloy, 1 P.3d at 1282-84, 1288-89; Donlun, 527 P.2d at 474.
. See Malloy, 1 P.3d at 1282-83, citing and discussing Huf v. State, 675 P.2d 268, 271-73 (Alaska App.1984).