The gunman who shot a security guard at the offices of right-wing think tank the Family Research Council last summer planned a mass killing due to what he considered to be the group’s “anti-gay” stance, The Washington Post writes.

The details about Floyd Lee Corkins II’s motivation in the August 15 shooting emerged in court papers Wednesday as the 28-year-old pleaded guilty to felony assault and weapons charges.

Mr. Corkins, who had volunteered at a gay community center in Washington, told investigators he was angry at the vocal opposition to same-sex marriage of the council and the owners of fast-food chain Chick-fil-A and planned to kill “as many people as possible.” The assault was foiled by the wounded security guard, who managed to wrestle the gunman to the ground.