A 19-year-old from Maine who the FBI says built homemade explosives and plotted to attack a mosque in the name of the Islamic State group was sentenced Monday to 15 years in prison.

Xavier Pelkey, of Waterville, entered an agreement with prosecutors in April in which he pleaded guilty to providing material support to terrorists while a second charge was dropped.

Pelkey planned to contribute firearms, ammunition and explosives for a mass shooting at a Shiite mosque in the Chicago area and possibly other houses of worship, and he was in communication with a pair of juveniles, one in Canada and one Chicago, about the plot, law enforcement officials said.

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Investigators found a handwritten document about the planned mosque attack. (Maine News)

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Pelkey was 18 when he was arrested by FBI agents who found three homemade explosives in his home. The devices were made of fireworks bundled with staples, pins and thumb tacks to create shrapnel, the FBI said. Investigators also found a handwritten document about the planned mosque attack, claiming it in the name of the Islamic State group.

The defense argued for a six-year prison sentence, contending Pelkey accepted responsibility, lacked a violent criminal history and was just a few months beyond being charged as a juvenile.

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Prosecutors produced a powerful narrative that the teenagers represented a homegrown terror cell, but an argument could be made that the teens were simply feeding off each other’s online bravado, said Chris MacLean, Pelkey’s lawyer.

“It seemed like a farfetched, quixotic teenager adventure,” he said. “That’s another narrative.”