New York City prosecutors announced the indictment of a man accused of gunning down his ex as she walked their 3-month-old in a stroller down an Upper East Side street last month.

Isaac Argro, 23, allegedly ambushed and killed Azsia Johnson, 20, on June 29.

"As alleged, Isaac Argro murdered Azsia Johnson, the mother of their 3-month-old child, in a premeditated act of fatal domestic violence"  Manhattan District Attorney Alvin Bragg said in a statement. "Committing this type of killing in front of an infant is horrific, and I cannot imagine the pain that Ms. Johnson’s family and loved ones are experiencing. I want to make clear that we will pursue full accountability and justice in this case." 

The indictment comes three weeks after NYPD Commissioner Keechant Sewell and Mayor Eric Adams visited the crime scene and vowed justice.

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Officers arrive on scene

Police arrive at the scene of a shooting on New York City's Upper East Side on June 29 that left one woman dead. (Citizen)

"We're going to find this person that's guilty of this horrific crime," Adams told reporters on the night of the murder. "We're going to find him and bring him to justice…to make sure that innocent person receives that justice."

Argro allegedly told Johnson to meet him near the intersection of East 95th Street and Lexington Avenue to give her some items for their daughter, according to prosecutors.

Johnson, possibly fearing for her safety, sent text messages describing "exactly where she was meeting the defendant and what he was wearing when she saw him," according to prosecutors. 

Instead of dropping off baby clothes, Argro was hiding there in dark clothes and a ski mask, authorities said.

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Alvin Bragg speaks during a news conference

New York City District Attorney Alvin Bragg speaks during a news conference at the Supreme Court after the exoneration proceeding of Steven Lopez, a co-defendant of the Central Park Five case, in New York City, New York, U.S., July 25, 2022.  (Reuters/David 'Dee' Delgado)

Then he allegedly shot her in the head at point-blank range and fled on foot, ditching his clothes as he ran.

Police responded to the scene almost immediately, according to a neighbor who told Fox News Digital he heard the gunshots from his living room that evening.

"I think that people should know how quickly they responded to her being shot," David Sivella said Wednesday. "That was in minutes."

He also showed video of the victim being rushed into the back of an ambulance. The shooting happened just outside an elementary school playground.

"Afterwards, Argro called Johnson’s family and inquired about the whereabouts of his child," Bragg’s office said in a statement. "He also threatened another individual who knew Johnson, saying they were ‘next.’"

Police traced his phone to an apartment in Brooklyn and arrested him there.

Argro faces charges of second-degree murder and two counts of criminal possession of a weapon. 

The baby was uninjured in the incident.

Police cars on scene

Azsia Johnson, 20, was gunned down near Lexington Avenue in the Upper East Side while walking with her 3-month-old. (Citizen)

Prosecutors said during a bail hearing earlier this month that Argro had a history of domestic violence and had assaulted Johnson when she was seven months pregnant. When police arrived, Argro was not there, but she was "crying with bruises to her face," prosecutors said.

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There was an open criminal complaint regarding that incident at the time of Johnsons’ death.

"The defendant very clearly planned on assassinating the mother of his child prior to meeting up with her and carried the gun with him to meet up with her," prosecutors told the court. 

Argro had no prior criminal record in adult court – but prosecutors revealed a juvenile record including sexual misconduct, possession of stolen property and petit larceny. 

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He was remanded without bail.

Fox News’ Adam Sabes contributed to this report.