Cheron Shelton is escorted Thursday from police headquarters. Shelton and Robert Thomas were charged with multiple counts of criminal homicide.

PITTSBURGH — Two men ambushed a backyard cookout near Pittsburgh, killing a pregnant woman, her 8-month-old fetus and four other adults, because they wanted retribution for the 2013 slaying of a friend, authorities said.

Cheron Shelton, 29, and Robert Thomas, 27, have each been charged with six counts of criminal homicide for the March 9 ambush in Wilkinsburg, Allegheny County District Attorney Stephen Zappala Jr. announced Thursday.

Thomas fired 18 shots from a .40-caliber pistol into about 15 partygoers, prompting them to run toward a rear porch, Zappala said. That’s where Shelton, hiding behind a fence, peppered them from five feet away with 30 shots from a rifle similar to an AK-47, killing the victims, Zappala said.

Shelton blamed Lamont Powell, one of three people wounded, for killing his best friend three years ago, Zappala said. Nobody’s been charged in the 2013 killing, though police have called Powell a suspect.

Two unnamed jailhouse witnesses, who spoke with the suspects after they were taken into custody on unrelated charges weeks after the shooting, described Shelton’s alleged bloodlust, according to criminal complaints.

One of the witnesses said Thomas indicated Shelton wanted to shoot more people at the cookout victims’ funerals, but Thomas claimed to have talked him out of it.

“I’m trying to treat them like the Jews; I’m trying to eliminate their whole blood lines,” Thomas told the witness, quoting Shelton’s intentions, according to police.

A second witness said Shelton “told him he was ‘hitting them’ with the ‘chopper”’ — street slang for an AK-47 — “and that he wanted everyone gone,” investigators said.

Thomas also expressed remorse to the witness, authorities said. The witness quoted Thomas saying: “Yeah, it’s killing me, crushing me every day. I’m trying not to think about it. I’m trying not to become a vegetable.”

Thomas’ attorney, Casey White, said he wouldn’t comment on the accusations until after he reads the complaint and talks to his client.

He and Shelton’s lawyer previously said their clients were innocent.

Earlier this week, the men’s attorneys attempted to get Shelton and Thomas out of jail, claiming both were unfairly being kept in solitary confinement to “squeeze” them for information on killings they knew nothing about.

Police haven’t found either weapon.