But their plea deal with prosecutors spared the teens any jail time.
Instead, they entered plea in abeyance agreements that required each of the young defendants to complete 200 hours of community service and stay out of trouble for 12 months. If they can do that, the charges will be dismissed and wiped from their records.
It was a huge relief for the teens and their supporters, about 50 of whom filled up the courtroom gallery Thursday morning.
"I wish I had support like that," marvelled an onlooker.
"Don't we all," answered the woman to her right.
One by one, the four defendants stood before Judge Andrew Stone to accept their sentences.
Gill went first.
"Ms. Gill admits she possessed a component of a chemical device," defense attorney Wally Bugden told the court Thursday.
"I plead guilty," the former beauty queen said.
She was followed by Bryce Christopher Stone, Shanna Marie Smith and, finally, John Patrick Reagh.
All were initially charged with four second-degree felony counts of possession of an explosive device. If convicted, the teens could have faced up to 15 years in prison on each count.
According to court documents, the four friends drove around Riverton neighborhoods on the evening of Aug. 2, throwing bombs they had made by mixing aluminum foil and toilet-bowl cleaner inside plastic bottles.
According to a probable-cause statement released by the jail, the first report arrived about 10:50 p.m. When authorities arrived, they found four plastic water bottles with remnants of aluminum foil and a chemical substance that had been detonated in a driveway and roadway near a residence.
Their intended targets were other friends, the documents state, and the bombs were meant as a prank.
Gill resigned her title after she was charged in the bombing case.
Bugden has said that the alleged victims in this case have written letters to prosecutors claiming there is no ill will between them and the accused. No one was injured. All four teenagers allegedly confessed at least once in interviews with police to having thrown a bomb.
"These are all nice kids who've never been in trouble," Bugden has said. "[They] did something that in hindsight they shouldn't have done."