Two men have been arrested - one of them after a gun battle with police - for the "cartel-style execution" in California last month of a family, including a teen mother and her baby.
Angel Uriarte, 35, was wounded in a shootout with police as he was detained and was having surgery, said officials.
Noah David Beard, 25, was taken into custody without incident. Their alleged motive remains unclear.
The six victims were gunned down on 16 January in the rural town of Goshen.
Both suspects were detained early on Friday and face six counts of murder and other crimes.
"I'm happy we were able to put these two men behind bars," said Tulare County Sheriff Mike Boudreaux, adding that Mr Uriarte was expected to survive an exchange of fire with federal agents.
He added that the suspects and members of the victims' families were known to have a long history of gang violence.
Four generations of one family - ranging in age from 10 months to 72 - were killed in the attack in the San Joaquin Valley.
Authorities had offered a $10,000 (£8,297) reward for information leading to the suspects' arrests.
Mr Boudreaux said the manhunt was known as "Operation Nightmare", and it involved around-the-clock surveillance of the suspects and multiple search warrants, some of which included inmates' cells in state prisons.
The county sheriff said one of the victims, teenage mother Elyssa Parraz, 16, had just days earlier been reunited with her 10-month-old baby, Nycholas Parraz, who had been living in foster care.
The baby's grandmother and great-grandmother were also among the victims, police and family say.
At a news conference in January, Mr Boudreaux said the child and mother appeared to have been fleeing the scene, and that forensic evidence showed the killer had stood over the victims and fired at their heads from above.
A few survivors remained at the "horrific" scene when officers arrived, he said.
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