CASTLE ROCK (AP) — A bomb squad late Monday detonated a pair of explosive devices found inside a suburban Denver home after the arrests of two teenage boys a day earlier, authorities said.

The items were “dangerous but required additional manipulation or steps to become actual bombs,” Douglas County Sheriff’s Capt. Darren Weekly told reporters gathered in the Castle Rock neighborhood where the discovery prompted the evacuation of more than 30 homes. Investigators dug holes behind the house in which to detonate the devices because it was too dangerous to move them much farther, he said.

The investigation began after an officer discovered a small box of suspicious chemicals inside the home of one of two teenagers who had been arrested for an unrelated reason Sunday night. The officer had gone to the home to notify the boy’s parents of his arrest when he spotted the items and requested a hazardous materials team, Castle Rock Police Chief Jack Cauley said.

Agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives joined the investigation.

The teens were arrested after neighbors reported them behaving suspiciously, and they remained in custody Monday night on charges unrelated to the discovery of the chemicals. Cauley said one of the boys, who are both about 16 years old, had “an extensive knowledge of chemicals” but he would not elaborate.

Authorities refused to provide other information about the teens because they are juveniles. The boys’ families are cooperating, Cauley said.

Police planned to work late into the night to determine whether there was any further danger.