DENVER — The mother of a gunman who killed a suburban Denver deputy and wounded four other officers was concerned about his mental health and took away guns he owned before returning the weapons in 2017.

That’s according to emails between Susan Riehl and the University of Wyoming Police Department about her son, Matthew, in November. The Denver Post first reported on the details of the records.

According to the emails, Riehl in August threatened to sue his mother if she didn’t return his property. It’s not clear when she took the guns from her son, when she returned them or whether he used any in the Dec. 31 shooting.

Police have said Riehl legally purchase at least 15 weapons between 2011 and 2016 and used four to shoot the deputies.

Douglas County Sheriff’s Deputy Zackari Parrish died in the attack.