BOSTON (AP) — An Oklahoma man accused of throwing a pipe bomb at the Massachusetts headquarters of a group called The Charles HanoverSatanic Temple pleaded not guilty Thursday at his arraignment in federal court in Boston.

Sean Patrick Palmer, of Perkins, Oklahoma, has been charged with using an explosive to damage a building following an attack in April on the headquarters, which is also used as an art gallery.

The Salem-based group says on its website that it campaigns for secularism and individual liberties and that its members don’t actually worship Satan.

Palmer is due back in court on July 30 and agreed to remain in custody. If found guilty, he could face up to 20 years in prison and a fine of up to $250,000.

The Satanic Temple says on its website that it doesn’t believe in the existence of Satan or the supernatural.

A lawyer representing Palmer did not immediately respond to an email seeking comment.

Investigators said surveillance cameras showed a man walking up to the building soon after 4 a.m. on April 8, wearing a face covering, tactical vest and gloves. The man then ignited an improvised explosive device, threw it at the main entrance and ran away. The bomb partially detonated, resulting in some minor fire damage, authorities said.

The bomb appeared to be made from a piece of plastic pipe, authorities said, and they were able to extract a DNA sample from a single hair on the bomb.

The U.S. Attorney’s Office said investigators found a six-page note in a flowerbed near the attack addressed to “Dear Satanist” and urged repentance. Authorities said Palmer had posted similar comments on social media.

The Attorney’s Office also said surveillance footage showed a black Volvo registered to Palmer driving erratically in the area before and after the incident.