DENVER (AP) — The parents of a 16-year-old boy who wounded two students at a Colorado high school with an old revolver his family said was kept in a locked gun safe won’t be charged with any crimes, authorities said Wednesday.

Investigators looked at whether the parents of Desmond Holly, who killed himself after opening fire, could possibly be charged with allowing access to the Smith & Wesson .38 special revolver or for not storing it safely, but decided there wasn’t enough evidence for that, the Jefferson County Sheriff’s Office said.

Holly shot himself after opening fire at Evergreen High School on Sept. 10 and later died.

Investigators didn’t find the parents’ DNA on the gun after getting a court order to collect DNA samples from them, the sheriff’s office said. It said the family’s lawyer recently told investigators that the gun, described as a family heirloom that had been owned by a grandparent, was kept stored near the back of a large, locked gun safe, the office said. Holly didn’t have access to the safe except for brief times when it was opened by his father, according to the lawyer.

The family’s lawyer, Douglas Richards, told The Associated Press the family believes Holly must have secretly taken the gun, which was never used, from the safe while he was cleaning other firearms with his father.

“Its disappearance didn’t become apparent until after the tragedy,” Richards said.

The sheriff’s office said investigators weren’t able to speak with the parents. Richards said the parents spoke with authorities right after the shooting and later answered questions in writing because he didn’t want them interviewed further unless there was a prosecutor present.

Investigators believe Holly randomly shot at students at the high school in the foothills about 30 miles (50 kilometers) west of Denver, sheriff’s office spokesperson Jacki Kelley said Wednesday.

At the time, the sheriff’s office said that Holly had been radicalized by an unspecified “extremist network.”

Kelley said the investigation showed that Holly had an obsession with other school shooters and had engaged with a mix of online groups but was not committed to any particular kind of radicalization. She referred further questions about those findings to the FBI, which handled that portion of the probe. The agency said a reporter would have to file a records request to obtain more information.

A report by the Anti-Defamation League’s Center on Extremism found that Holly had been active on an online forum where users watch videos of killings and violence, mixed in with content on white supremacism and antisemitism. It found Holly was also fascinated with previous mass shootings including the 1999 Columbine High School massacre that killed 14 people, about 20 miles (32 kilometers) away from Evergreen.