A Utah teenager was arrested after authorities say he lied about seeing a man with a gun inside his high school, triggering a two-hour lockdown and massive police response that illustrated a climate of fear amid repeated mass shootings.

Parents and residents in the small city of Pleasant Grove, Utah -- about 35 miles south of Salt Lake City --waited nervously outside the school Thursday afternoon after finding out about the lockdown in emails and automated calls from the school district.

Inside, SWAT-team officers carrying guns ordered anxious and confused students into the gym and did a room-by-room search.

Police didn't find any weapon or gunmen. As they questioned the 15-year-old boy who made the report, it became clear it was a hoax.

The teenager, who is not being named, was arrested on suspicion of making a false report and terroristic threats. He told a school administrator that he saw a man wearing a trench coat and carrying a gun, said Pleasant Grove Police Capt. Michael Roberts.

After questioning, he eventually acknowledged it was made up. He didn't say why he did it, but police speculate it was to get out of a class activity he didn't want to participate in, Roberts said.

A total of 200 officers from several law enforcement agencies in the area flooded the school, fearing that it could be the latest mass shooting, following the rampage earlier this week in California. They sent an armored vehicle. One of the officers rushing to the scene got into a traffic accident on the way, police said.

Police opted to arrest the teenager and pursue charges to send a message that it's not OK to use up so many valuable law enforcement resources and cause so much stress and fear among students and parents, Roberts said.

In the last several decades, police have been trained to take every report seriously and respond as if it's legitimate, Roberts said.

"You're thinking worst case scenario and you're preparing for that," Roberts said. "You don't know if it's one person or five people -- if it's guns, bombs."

Alpine School District spokeswoman Kimberly Bird said the school will determine whether to take disciplinary action when he returns. The boy is currently in a juvenile detention center. She said he's had some issues that required meetings with administrators but nothing this serious.

"Your heart just goes out to this student: Did he really understand what ramifications were going to come about?" Bird said. "I'm sure if the student could take it back, he would. But we live in a day and age where there's going to be consequences for things like this."

After the lockdown was lifted, students at Pleasant Grove High School were let out of the school one class at a time. Relieved parents were waiting, leading to some tearful embraces, the Daily Herald newspaper in Provo reported.

Rolando Ruelas and Christian Anderson sat in their classroom for more than an hour wondering what was happening until police came to their room.

"We weren't sure if it was real or not," Ruelas told the Daily Herald. "But then we got a knock on the door and a note slipped under the door from the police. Then a SWAT guy came in."

Students and parents were on high alert after Wednesday's mass shooting in San Bernardino, California, that killed 14 people.

Parent Camie Miller received a text from one her twins at the school that policed had come in with a dog and search bags, locked the door behind them and left.

"With everything that happened in California yesterday, I'm glad they're being overcautious," Miller told the Daily Herald.