DENVER (AP) — Denver police say they have arrested a man suspected of killing three homeless people who were found shot to death in a parking lot.

Authorities say 38-year-old Maurice Butler was arrested Thursday on suspicion of three counts of first-degree murder. Formal charges have not been filed yet. It's not clear if Butler has an attorney to comment on his behalf.

Police say Butler knew at least two of the victims. They say the killings were "not a random incident," but they have not discussed motive.

Online jail records show Butler has been in custody since Aug. 13, when he was arrested for possession of a controlled substance.

Authorities previously identified the victims as 28-year-old Nicole Boston, 39-year-old Jerome Coronado and 45-year-old Christopher Zamudio. Their bodies were found on Aug. 9.