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PITTSBURGH — Prosecutors in Pennsylvania say they plan to seek the death penalty against two men charged in an ambush at a cookout that killed five adults and an unborn child.

The Allegheny County district attorneys' office filed notice Friday that it would seek capital punishment if Cheron Shelton, 29, and Robert Thomas, 27, are convicted of first-degree murder.

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Prosecutors said the death penalty would be warranted because of the defendants' previous convictions, the multiple felonies alleged and the grave risk posed to others.

Cheron Shelton and Robert Thomas. Allegheny County Police

Defense attorneys say the men are innocent. Shelton's lawyer, Randall McKinney, called the decision to seek capital punishment "disheartening," but said it didn't shake his belief that his client's name will be cleared at trial.

The men are each charged with six counts of criminal homicide in the March 9 cookout in Wilkinsburg, a suburb of Pittsburgh. Prosecutors suspect a man wounded at the cookout had killed Shelton's best friend in 2013, and they are looking for that man.

Prosecutors allege Thomas fired 18 shots from a .40-caliber pistol into a group of about 15 partygoers, prompting them to run toward a rear porch where authorities say Shelton was hiding behind a fence. Prosecutors allege Shelton peppered the fleeing crowd from 5-feet away with 30 shots from a rifle similar to an AK-47.

Brittany Powell, 27, who was renting the home, was killed as were her siblings Chanetta Powell, 25, and Jerry Shelton, 35. The county medical examiner ruled Chanetta Powell's unborn son died because of her death. The siblings' cousin, Tina Shelton, 37, and their friend, Shada Mahone, 26, also died in the attack.

The two men also face charges of criminal conspiracy, aggravated assault and reckless endangerment. Authorities say bullets pierced the walls of the residence, wounding three other people. Three children were in the house at the time but unharmed.