One Lakewood police officer was killed and three officers were wounded Thursday evening after police responded to a call involving a public bus in Lakewood, Colorado, according to the Associated Press.

Police spokesperson John Romero said the initial call concerned a person attempting to board a bus. The Regional Transportation District identified the vehicle as a contractor-operated Route 76 bus at West Colfax Avenue and Wadsworth Boulevard.

RTD said its personnel responded to the scene and were cooperating with Lakewood police. The transit agency identified the police department as the agency conducting the investigation.

Sources: RTD statement and Associated Press reporting.