Three sixth-grade boys had a "hit list" and were plotting to kill fellow classmates on the last day of school in a sniper attack during a false fire alarm, police said.

The plan was modeled after a recent ambush at a Jonesboro, Ark., school that left five dead, Lt. Dave Todd said.Police learned of the plan after they responded to a fight at Becky David Elementary School in rural St. Charles County on Thursday. Todd said what officers found was far more serious than a schoolyard brawl.

The boys planned to pull a fire alarm and then shoot students as they fled the school, Todd said. He said they got the idea from the March 24 incident in Jonesboro, where an 11-year-old boy and his 13-year-old friend allegedly opened fire on classmates after pulling an alarm. Four pupils and a teacher were killed and 10 people were wounded.

The sniper attack at Becky David Elementary was to be carried out on June 6, the last day of school.

"We tend to think this was going to happen," Todd said. "The only thing missing was the gun."

One of the boys, described as the leader, claimed to be familiar with guns and was working to locate a rifle, which could be used to shoot students from long-range, Todd said.

He was being held Thursday night by juvenile authorities. The other two were released to their parents.