By Greg Argos

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PHILADELPHIA (CBS) — The family of a murdered Philadelphia police officer is frustrated by the legal system, after the killers of Philadelphia Police Sgt. Robert Wilson III cut a deal with prosecutors to avoid the death penalty.

Philadelphia District Attorney Larry Krasner called the sentence “death by incarceration” – a sentence the sergeant’s family says is unacceptable. Brothers Carlton Hipps and Ramone Williams will spend the rest of their lives in prison with no chance of parole.

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“It’s horrible. A total slap in the face,” said Officer Damien Stevenson, Wilson’s former partner.

Wilson and Stevenson pulled up to a North Philadelphia GameStop on March 5, 2015 because Wilson wanted to buy something for his son’s birthday.

Hipps and Williams shot Wilson six times while attempting to rob the store. Wilson returned fire and protected other shoppers inside.

“He was actually on the ground when shots were still being fired at him,” said Philadelphia Police Commissioner Richard Ross.

The violent murder was caught on surveillance video.

Stevenson, Wilson’s sister, his grandmother, the Fraternal Order of Police and even the police commissioner all expected the two to face the death penalty.

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However, at Monday’s plea hearing, Krasner argued life in prison would spared Wilson’s children the trauma of a trial and seeing the video of their father’s killing.

The DA says his decision was based on what the mothers of his children wanted, despite the objections of other family members and fellow officers.

“They do that whether they have a sentence of death by incarceration, which is life without the possibility of parole, or they have the sentence of death. It’s the same outcome,” said Krasner.

“The DA calls this death by incarceration, I consider it justice deferred. These men don’t deserve to share this city or this earth with us,” said Officer Michael Rivera, who went to the Philadelphia Police Academy with Wilson.

“I’m disgusted. This in no way is what my brother deserved. He gave his all,” said Wilson’s sister, Shaki’ra Wilson-Burroughs.

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The family was also upset that Krasner left the hearing before family statements even began. During a tense plea hearing, 11 members from Wilson’s family, friends and fellow officers voiced their displeasure about the DA’s decision.

“Yes, it was entirely appropriate,” said Krasner. “I was actually dealing with matters in this case that were developing.”

Krasner says those matters included witness intimidation, indicating the Fraternal Order of Police had harassed the mothers of Wilson’s children in an attempt to persuade them to change their mind about the plea deal.

“If things get bad enough, I may have to take legal action about them,” said Krasner.

Krasner says an investigation is ongoing.