Device at school believed to be IED determined to be harmless plastic bottle: Sheriff Students were evacuated after the bottle was found on the playground.

A device found at a Montana elementary school on Tuesday that authorities initially said was an explosive actually turned out to be a plastic bottle covered in tape, police said.

"This information is good news," Lewis and Clark County Sheriff Leo Dutton said at a news conference Tuesday afternoon. "It's a blessing that it wasn't [an explosive]."

The Tuesday-morning announcement of an improvised explosive device detonating on the playground of the Rossiter Elementary School in Helena sent FBI and ATF agents to the scene. Students were evacuated. No one was injured.

Dutton said Tuesday afternoon that authorities determined nothing ever exploded. The device, believed to have come from a construction site, was a plastic bottle wrapped in black tape that was full of washers, nuts and bolts, and a fluid that wasn't flammable, the sheriff said.

A homeless man, who didn't have malicious intent, thought he was picking up litter and placed the bottle by the school Monday night or early Tuesday, Dutton said. No charges are expected to be brought against the homeless individual.

The sheriff defended authorities' actions and said they "handled it appropriately" by announcing an IED had been found Tuesday morning.

"I am glad our team here, local, state and federal, reacted in such a way," Dutton said.

Witnesses initially described to authorities seeing a debris field, leading them to believe something had detonated, the sheriff later told ABC News in a phone interview.

"When we were first told that there was what appeared to be an unexploded device, we responded," he added. "Then later, people who were at a distance described what they saw as a debris field. They said, 'Looks like it had exploded.' So that's the information that was released to me."

Helena District 1 Schools and East Helena Schools were placed on lockdown earlier Tuesday as law enforcement searched the buildings. The schools were later cleared and the lockdowns were lifted.