TOLEDO, Ohio (AP) — A man accused of plotting with his girlfriend to obtain guns and explosives for a foiled domestic terror attack pleaded guilty to a federal conspiracy charge.

Prosecutors said the pair had talked extensively about taking part in violent attacks on public places, visited the site of the Columbine High School massacre, and had bomb-making materials and weapons.

Vincent Armstrong, 23, of Toledo, pleaded guilty Thursday to a charge related to conspiring to transport or receive an explosive with intent to cause harm. He faces up to 20 years in prison, but his sentencing has not been scheduled.

Armstrong had a duffel bag in his car filled with ammunition, a tactical vest, a trench coat and a T-shirt that said “society failed us,” federal authorities said in court documents.

His defense attorney declined to comment on Friday.

Authorities allege Armstrong’s girlfriend, 23-year-old Elizabeth Lecron, drove the plans. She has pleaded not guilty and her attorneys have not commented since her arrest in December.

Investigators said they found journal entries in which the pair discussed an attack. Lecron wrote about a mass killing at a bar along with an attack at a livestock farm or where she had worked, according to court documents.

The filings said the couple traveled to Colorado last August to see Columbine High School, where two students killed 12 classmates and a teacher in 1999. While away, the FBI searched their home in Toledo and said they found an AK-47, a shotgun and a stockpile of ammunition.

Lecron was arrested when she bought supplies for a bomb after undercover agents told her they wanted to blow up a pipeline, documents said.