MANSFIELD (AP) — A 28-year-old man is expected to plead guilty to posting on an FBI website that he planned to kill President Barack Obama.

Andrew O’Keefe, of Mansfield, is scheduled to appear in Boston federal court Dec. 15 to change his initial not guilty plea. He’s been charged with posting an online threat against the president.

Prosecutors say that on May 13, 2015, O’Keefe wrote on the FBI tips site that he was “planning to kill President Barack Obama” and had “a really good plan.” He invited the Secret Service to pay him a visit and signed the posting with his Social Security number.

Authorities say they found over 100 weapons in O’Keefe’s home and vehicle, including swords, double-edged knives, hatchets and spears. His lawyer did not immediately comment.