Among the dead were four police officers from three different agencies, Sandoval said.

"This is the worst violence we've seen this year," he said, referring to the three days from Thursday through Saturday.

The bloodshed started on Thursday with 14 people killed, including a municipal police officer.

Friday was the most violent day, leaving 20 people dead. A municipal police officer was killed by an assassin who belonged to a band of carjackers. Hours later, a state police investigator was executed on his drive home.

On Saturday, a highway police officer was killed by a driver who confronted the patrolman after the officer gave him a ticket. The officer was shot 10 times at close range in the middle of the afternoon. In all, 19 people were killed that day in separate shootings throughout the city.

Elsewhere on Sunday, Mexico's Public Security Secretariat reported that 13 taxi drivers were killed in the resort town of Acapulco in a rash of violence that began early Friday.