Two Men Arrested in Execution-Style Killings of a Family in California

“Governor, we arrested the perpetrators. We are asking you to do your part,” the sheriff said on Friday.

Mr. Boudreaux said that the 16-year-old, Alissa Parraz, had fled with her baby, Nycholas, when she heard gunfire. Surveillance video played at the news conference showed her placing her son on the other side of a fence and leaping over. Then, both mother and infant were shot in the back of their heads by Mr. Beard, the sheriff said, and found dead in the street by the police.

The gunmen also killed Mr. Parraz’s mother, Rosa Parraz, 72, when she was on her knees, the sheriff said. The other victims were Mr. Parraz’s son, Marcos Parraz, 19, who was not in a gang; and Mr. Parraz’s girlfriend, Jennifer Analla, 50, who was asleep when she was murdered, the sheriff said.

Police had visited the family’s home with a drug search warrant a week before the ambush and found marijuana, methamphetamine and weapons. The 52-year-old Mr. Parraz, a felon, was arrested and released four days later after posting bail.

More than 30,000 gangs, representing more than one million people, operate in the United States, according to the F.B.I. The groups have increased their sophistication, organization and mobility in recent years. They also work closely with Mexican drug cartels that control the export of illicit substances to the United States across its southern border.

In the Central Valley, cartels are believed to collaborate with local Latino, Black and Asian criminal organizations that often buy drugs wholesale from them.

The Norteños and Sureños gangs have deployed members across the United States to expand their territory and increase drug sales. As a result, many suburban and rural areas face problems similar to those once confined to big cities.