LAWRENCE — Lawrence police are reviewing videos from security cameras at Bruce School to determine the identity of three people who set up bombs inside coke bottles in the schoolyard.

School custodian Brian Susi found two bottles in the middle of the schoolyard with a white substance around them when he arrived for work at 6:05 a.m. yesterday.

Susi notified school safety officer Jim Malloy, who in turn called city police.

Police Chief John Romero said the trio, who were wearing dark clothes and appeared to be teenage boys, went to the school with the sole purpose of setting off the device.

"We believe they are not students at the school and did not know there were surveillance cameras," Romero said.

The video shows three people entering the schoolyard at 1:24 a.m. and walking toward the school, according to the report filed by police Lt. Sean Burke.

At 2:15 a.m., three shadows emerged from the school and two minutes later, three people walk to the center of the yard, place two objects on the ground and run. Two bottles explode at 2:18 a.m., as seen on the video.

Romero said he believes the suspects were making the bomb while out of view of the surveillance camera. Neighbors reported hearing shots fired around the same time the bombs went off.

Police are enhancing the image on the video to get a better look at the suspects' faces. The soda bottles recovered at the scene were sent to the crime lab for analysis. Romero said teenagers are finding the recipe for bottle bombs on the Internet, or are learning it from their friends.

"Some are doing it for kicks, but this is not a kid's game. It can be dangerous and they can hurt themselves or someone else, if it explodes," Romero said.

The bombs are made by combining certain household ingredients in a plastic bottle. The combination of the ingredients creates a chemical reaction under pressure inside the bottle, making it explode.

Romero said it is the third time this year police have found bottle bombs.

In February, police discovered two bombs — one outside 308 Jackson St. and another outside 245 Bruce St.

In March, three Oliver School students made bottle bombs, injuring one of the boys who was holding the bottle at arm's length when it exploded.

In addition to the possible property damage and physical danger to themselves, there also are criminal consequences if caught making bottle bombs. Romero said people can be charged with illegal possession of an explosive item.

"This is a crime and it's serious," he said.