A clear motive behind the attack, described by prosecutors as an act of “political extremism,” remains unclear.

A Minnesota man plans to plead not guilty to charges he killed the top Democratic leader in the state House and her husband after wounding another lawmaker and his wife, his attorney said.

“This political assassination, the likes of which have never occurred here in the state of Minnesota, has shaken our state at a foundational level,” acting U.S. Attorney Joseph Thompson said.