A West Philadelphia woman brought a gun to an argument in Lower Merion Township on New Year’s Eve, according to investigators. Her mother had asked for help, saying her fiancé had hit her during a heated dispute at a bar.

And when Samiyah Williams arrived at the Delwyn Apartments in Bala Cynwyd to check on her mother, she herself got into an argument with Adrionne Reaves, police said, shot him once in the head, and left him and her mother in the apartment’s crowded lobby.

After days of searching by Montgomery County detectives, Williams, 24, turned herself in to police early Monday. She has been charged with first- and third-degree murder and possession of a weapon.

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Williams remained in custody, denied bail. Her attorney, Prince Paris Amor Holloway, did not immediately return a request for comment.

Officers in Lower Merion first encountered Reaves and Joi Furman, Williams’ mother, about 8:30 p.m. Friday, when a bystander called 911 after seeing the couple arguing, according to the affidavit of probable cause for Williams’ arrest. The couple told the officer their argument was not physical, and, after separating the two, the officer left to handle another call.

Hours later, that same officer returned to the Delwyn Apartments to a homicide scene.

Reaves, 45, was pronounced dead at the scene by medics, the affidavit said. In an interview with police, Furman, 43, explained that her daughter had shot Reaves, that her daughter “has a bad temper,” and that she was terrified over losing Reaves and possibly her daughter.

Williams came to the apartment only after Furman had called her mother — Williams’ grandmother — earlier that evening after Reaves struck Furman during an argument, the affidavit said. Williams and her grandmother drove to Furman’s apartment, bringing a 9mm Walther handgun that Williams is registered to carry in Philadelphia.

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Surveillance footage from the lobby of the apartment shows that Williams started an argument with Reaves, then shot him once before running out of the building and driving off, according to the affidavit.