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PITCAIRN (KDKA) — The man accused of fatally stabbing his girlfriend at her Pitcairn apartment Sunday night is now behind bars.

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According to Allegheny County Police, 59-year-old Derrick Avant turned himself into Rankin Police Wednesday evening.

(Source: Allegheny County Police)

He’s facing a charge of criminal homicide in the stabbing of 55-year-old Alison Fritzius.

Police say Fritzius was stabbed just before 7 p.m. Sunday in an apartment on Hillside Avenue and ran next door to her neighbor’s house to ask for help.

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The neighbor told KDKA she started banging on the door and asked him to call 911. When he asked her who did that to her, she answered, “My boyfriend D,” according to the neighbor.

Investigators believe Avant stabbed Fritzius following an argument. He then ran from the scene.

Insp. Andrew Schurman said this was not the first time that Avant tried to harm her, saying the couple “had an on again off again relationship and it was described by the Pitcairn Police Department as ‘tumultuous at best.’”

He added that there was a series or a history of domestic incidents with them and “she had a PFA against Mr. Avant, so we’re not sure what triggered him to go to the residence,” said Insp. Schurman, Allegheny County Police Department.

Avant has a lengthy prior criminal history. He’s faced charges for aggravated assault, harassment and drugs.

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Avant is now being held in the Allegheny County Jail. He has a court date next week.