A wave of violence is sweeping through the Mexican border city of Tijuana, which lies just south of San Diego.

Three high-ranking police officers were killed, along with the wife and child of one of the officers.

At a midday press conference at the police station, police officers hid their faces behind black masks and had their machine guns at the ready.

Grim-faced law enforcement officials descended from a parade of black, armored sport utility vehicles. They went inside to face a room that overflowed with reporters.

Tijuana's top security chief Alberto Capella recounted the events.

Officers Killed

Capella said it began with a call at 10:40 p.m. Monday reporting gunfire near one of Tijuana's main traffic arteries.

Officers arrived and found the district's police chief slumped over his steering wheel with half his face shot off. His second-in-command was in the passenger's seat, riddled with bullets.

Another high-ranking police commander was later found shot dead in his bed. His wife and the couple's 11-year-old daughter were also killed. Their 4-year-old daughter was wounded.

Police are tight-lipped about the details and motives for the murders. But Baja California's attorney general believes the case is tied to drug cartels.

Residents Fearful

This wave of violence comes as hundreds of federal police are streaming into Tijuana.

They're the second group of reinforcements Mexican President Felipe Calderon has sent to the city in a year to help tame the drug violence. Local law enforcement officials say the killings may be in retaliation for the crackdown.

Capella said what police are doing is working, but many Tijuana residents are fearful.

"We live with Jesus in our mouth," said Adriana Alvarado, as she pushed a stroller in downtown Tijuana. "Every time we walk out of the house, it's like, 'Oh, God, help us." It's like just saying, 'Hey, we're in your hands.'"

Local human rights activist, Victor Clark, is nearly as fatalistic.

He says the recent violence mocks officials' claims of success and predicts the crime could be long term because law enforcement officials appear powerless.

KPBS' Amy Isackson reports

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