Twin brothers have been arrested and charged in relation to a federal investigation which have turned up explosive-making materials.

Christian and Tyler Toro had been gathering bombmaking materials since last year and were arrested by the FBI on Thursday in the Bronx in New York City, according to a criminal complaint filed in federal court in Manhattan.

Christian Toro was a high school teacher in Harlem, but stepped down after a student reported a bomb threat on Dec. 4. After Tyler Toro returned Christian Toro’s school-issued laptop, a book on explosives was found on the computer.

Although authorities were notified, Christian Toro claimed he didn’t intend to download the book and had come across it while investigating the Boston Marathon bombing.

During a press conference Thursday night, which included the U.S. Attorney’s Office, the FBI, and New York police, New York City mayor Bill de Blasio said that there was no evidence to suggest a continued threat despite an ongoing investigation.

The FBI talked with several students who revealed that Toro had financially compensated them $50 an hour to disassemble fireworks and keep the gunpowder, according to the federal criminal complaint.

Toro’s apartment was searched by authorities, who recovered bombmaking materials, including 20 pounds of iron oxide, 5 pound of aluminum powder, 5 pounds of potassium nitrate, among others.

A diary was recovered that appeared to belong to Tyler Toro that claims, “We are twin Toros strike us now, we will return with nano thermite.”

A yellow backpack with an index card was also found that says, “Under the full moon the small ones will know terror.”