BOSTON — Police Commissioner William Evans says Boston police are on alert after police officers were murdered in New York City and Florida.

WCVB-5 reports Evans called the police attacks a “tragedy” and said it was “sad” that there is a “lot of anger” and “rhetoric being thrown around” against officers.

On Saturday, a gunman ambushed two New York City police officers sitting in their patrol car and then took his own life. Early Sunday, a police officer in Tarpon Springs, Florida, was shot and killed in a residential area.

The commissioner said Boston police assigned two officers to patrol cars for “several days” after a Missouri grand jury in November declined to indict a white police officer in the shooting death of an unarmed black teenager.