A 52-year-old New Haven man with a history of threatening behavior pleaded guilty Monday in U.S. District Court to mailing a white, powdery substance to the Islamic Center of New London in September 2018, and to six other charges of threatening to intimidate, injure or kill people in Connecticut and elsewhere.

Gary Joseph Gravelle, also known as Roland Prejean, faces up to 60 years in prison when he is sentenced March 26 by U.S. District Judge Kari A. Dooley in Bridgeport.

He pleaded guilty to five counts of maliciously conveying false information about an explosive, an offense that carries a maximum term of imprisonment of 10 years on each count; one count related to the sending of hoax Anthrax letters, which carries a maximum term of imprisonment of five years, and one count of making threats against the president, which carries a maximum term of imprisonment of five years.

According to the government, Gravelle mailed an envelope to the Islamic Center of New London, which is in Groton, containing a white, powdery substance and a piece of paper reading "You Die" and "Anthrax is an acute infectious disease caused by the spore-forming bacterium Bacillus anthracis, a category A agent."

Said Ali, a member of the mosque who helps with mosque operations and lives with his family in an attached home, said by phone Tuesday that he brought the envelope home and his children were present when he opened it and called police. Authorities investigated the incident as a hate crime.

Ali said the court had notified him of Gravelle's intention to plead guilty in exchange for a prison sentence.

"One part of it makes me think, 'OK,'" Ali said of the plea agreement. "But by the end of the day, it doesn't make me happy to see someone go to jail. I wish there was a different way to guide them and bring them closer to God."

According to court documents and statements made in court, in September 2018, Gravelle used U.S. mail, email and telephone to threaten to harm people and explode property in Connecticut, Vermont and Washington. Certain letters that Gravelle mailed contained a white powdery substance and statements that the substance was Anthrax, a biological agent and toxin.　

Gravelle made threats to various mental health providers and facilities in New Haven, U.S. probation officers, a U.S. District Court judge, an international airport in Vermont, a federal prison in Washington, occupants of a building in Old Saybrook, a credit union in Bristol, and organizations and religious centers in Connecticut. He also sent a letter threatening to kill the president of the United States.

At the time, he was on supervised release for similar crimes. On July 19, 2013, Gravelle was sentenced in Bridgeport federal court to 70 months of imprisonment, followed by three years of supervised release, for mailing numerous threatening letters in 2010. Gravelle was released from prison in 2015 and, in September 2018, was still under federal supervision.

In pleading guilty, Gravelle also admitted that he failed to comply with conditions of his supervised release, namely not violating any federal or state law by engaging in the threatening conduct in September 2018.

Gravelle has been detained since his arrest on Sept. 8, 2018.

The case was investigated by the Federal Bureau of Investigation, U.S. Marshals Service, U.S. Secret Service, and U.S. Postal Inspection Service, with the assistance of the U.S. Bureau of Prisons, Connecticut State Police, Connecticut Department of Energy and Environmental Protection, and many local police and fire departments, including departments from Bristol, Guilford, Groton, Hartford, Middletown, New Haven, Old Saybrook, Southington and Stamford, Yale University, and Burlington, Vt.　

The case is being prosecuted by Assistant U.S. Attorney Peter S. Jongbloed.