An 18-year-old accused of killing two people and wounding a juvenile at a Northern California library may have been inspired by the 1999 Columbine High School massacre, authorities said Tuesday.

Police alleged that Bradley Scott Sayer fatally shot Jacob Hull, 46, and Robert Johnson, 74, on Monday evening at a library in Chico, California. A female juvenile who was with Hull was hospitalized with a non-life-threatening injury and has since been released, said Chico Police Chief Billy Aldridge.

All three were library patrons.

Officers arrested Sayer less than four minutes after the first 911 call as he tried to flee out the back of the library, Aldridge said.

FBI Sacramento Special Agent in Charge Sid Patel said Sayer initially entered the library without a weapon before returning to his vehicle and retrieving a shotgun from the trunk.

Authorities said Johnson was shot near the library entrance before the suspect fired additional rounds inside the building. Hull also was fatally shot, investigators said. Patel said about eight shotgun rounds were fired.

Officers recovered a shotgun inside the library and found two additional firearms in Sayer's vehicle, Aldridge said. The weapons were registered to members of Sayer's family, he said.

At the time of the shooting, Sayer wore a white T-shirt scrawled in black marker with the words "natural selection," mirroring a shirt worn by Columbine gunman Eric Harris, Patel said.

Butte County District Attorney Michael Ramsey told reporters Sayer had been "a fan, and a fan for a long time" of Columbine-related social media content and had made what Ramsey described as a deep dive into that community. Detectives have found no prior relationship between Sayer and the victims.

The 911 call came in at 5:12 p.m., with dispatchers picking up gunshots and screams on an open line.

The first officer reached the scene at 5:14 p.m. By 5:16 p.m., Sayer was in custody, taken down by perimeter officers as he ran out the back.

"I absolutely believe that this is what mitigated further loss of life," Aldridge said. No officers fired their weapons.

Sayer is being held in isolation at the Butte County Jail on two open counts of murder and is scheduled to be arraigned Thursday in Oroville, Ramsey said.

His family has retained an attorney whose name has not been released.

Misty Wright, Butte County's director of libraries, said security personnel will be stationed at branches before they reopen.

California Gov. Gavin Newsom, a Democrat, and Assemblymember James Gallagher, R-East Nicolaus, issued statements praising law enforcement and mourning the victims.

The Associated Press contributed to this report.