A gang banger allegedly fatally stabbed his girlfriend and slipped away from the scene — then tried to throw cops off his trail by reporting the killing himself, according to police and the victim’s family.

Alicia Arnone, 35, was found in a pool of blood at the top of a staircase by her 13-year-old daughter, who had heard her mother’s screams, and the sound of someone leaving their Leonia home, Arnone’s family told The Post.

Cops quickly arrested the girl’s father, Andre Daniels, in her March 26 killing.

Daniels, who has a lengthy rap sheet, and Arnone dated on-and-off for 14 years, and he had a history of assaulting her, according to her family and reports.

When the cops arrived at the crime scene at the first-floor apartment on Grand Avenue, they found Arnone’s daughter along with the woman’s new boyfriend, Nile Diakos, 35, of Paterson, who had called police at 9:59 a.m. to report a stabbing, authorities said.

Both Diakos and the girl told police that Daniels, who had had restraining orders issued against him in the past because of abusive incidents involving Alicia, was the murderer, according to court papers cited by the Daily Voice.

In a chilling twist, police now believe that Diakos stabbed Arnone, slipped out of the house and circled back after calling police to report the murder. Charges against Daniels in the case have been dropped, and he was released from custody Wednesday.

Police received phone recordings of Diakos confessing to killing Arnone, court documents show. Diakos, who calls himself an “OG Cripp” and said he “studied at Trenton State Prison” on his Facebook page, was arrested Thursday and charged with first degree murder, police said.

The tragic mix-up was understandable on the part of Alicia’s daughter, Arnone’s mother told The Post Saturday, because the girl had witnessed her father’s abuse for so long.

Karen Arnone said the girl woke up when she heard her mother screaming and heard someone leaving the house.

“She didn’t see him but she thought it was her father,” Karen Arnone said.

Arnone said Daniels kicked the door in and beat up Alicia in December, and there were orders of protection against him forbidding him to go near either Alicia or their daughter but he ignored them.

Daniels had a 20-year criminal history involving assaults, threats, harassment and violating restraining orders, police sources told the Daily Voice last week. The outlet also reported that there had been multiple reports of domestic violence between Daniels and Arnone. A final restraining order was issued in 2021 to prevent any contact between the two.

“Alicia and Andre were together for so long,” her mother said. “She thought she could fix him. He beat her so badly in December. That’s why we all thought he was the murderer. We don’t really know this new guy.”

Diakos posted a tatted-up selfie on March 15, less than two weeks before Alicia’s murder, and wrote: “A chick says she loves u but then this,,,IMA get her bacc…”

The day after Alicia’s murder, Diakos posted a photo of her on Facebook.

“R.I.P. Alicia Arnone. Ur in the lords arms now…no more pain,” Diakos wrote.

Daniels did not return several phone calls and texts from The Post.