(CNN)Federal prosecutors have accused a Maine teen of plotting to attack a Chicago-area mosque and charged him with possession of a destructive device.
According to court documents unsealed on Friday, Xavier Pelkey, who was 18 years old when he was arrested on February 11, was charged by criminal complaint in Maine federal court for one count of possession of unregistered destructive devices.
CNN has reached out to an attorney for Pelkey for comment.
In the documents, an FBI agent said investigators found three items in a backpack that appeared to be handmade explosive devices. An initial review of the items found them to be fireworks taped together with staples, pins, and thumbtacks, which the FBI agent said were "designed to increase the amount of shrapnel propelled by an explosion" if detonated.
Prosecutors allege Pelkey planned to attack a Shia Muslim mosque in the Chicago area "during spring break" with a 15-year-old and a 17-year-old with whom he had been speaking on Instagram.
FBI Agent Garrett Drew alleges it was Pelkey's job to acquire additional firearms and ammunition and he allegedly "had built an explosive device 'to get more people,'" according to court documents.
Drew said in a declaration filed in February and unsealed Thursday that the Chicago-area 15-year-old told the FBI the three planned to enter the mosque, "separate the adults from the children, then murder the adults."
"If they had not encountered law enforcement at that point, they would continue on to another Shia mosque or Jewish synagogue and execute the same plan," the court filing states. "They did not have a plan to escape but rather their plan ended with them being shot by law enforcement."
Chicago FBI agents seized multiple firearms, swords, knives, a bow and arrows, multiple homemade ISIS flags, and multiple electronic devices from the 15-year-old's home while executing a search warrant in February, the court filing said.
Investigators also searched the home of a 17-year-old in Kentucky in February, who investigators believe spoke with Pelkey on Instagram, who told them Pelkey talked about "gathering materials to make fireworks to attack someone."
In the filing, Drew said the FBI investigation obtained information from Facebook for the Instagram account the two unnamed teens said they used to communicate, and then linked it to an IP address for Pelkey. The FBI searched Pelkey's home on February 11, he agreed to answer questions from investigators and confirmed he was the owner of the Instagram account, the filing states. Investigators found three homemade explosives and homemade ISIS flags.