KEIRA AVILES-RIVERA had decided she was going to get her life back on track by leaving her boyfriend and getting her GED.

But just a few days removed from her breakup, neighbors said, the situation turned tragic yesterday when the 19-year-old's deranged ex-boyfriend allegedly shot her in the face and shot her 21-year-old brother in the back about 2 a.m. in a house on Margaret Street near Torresdale Avenue. About an hour later, police shot the ex-boyfriend blocks away after they said he pointed a loaded gun at officers and tried to take a cop's service weapon.

Aviles-Rivera and her brother, identified by neighbors as Joezer Quinones-Rivera, were both taken to Hahnemann University Hospital in critical condition. The alleged shooter, identified by sources as Anthony Rivera, (no relation to the victims) was also listed in critical condition at Hahnemann.

"I ain't been to sleep since it started early [yesterday] morning," said next-door neighbor Markita Hines, who was awakened by the screams, followed by gunshots. "It's just unbelievable. I still can't believe it. She was so pretty . . . and the brother, he was a good boy. He was in the service."

Hines said the siblings had attended a Sweet 16 party for a neighbor's daughter Saturday night at K and Cayuga streets. The ex-boyfriend showed up about midnight as the party was winding down, but Aviles-Rivera had already left. He pulled out a gun, prompting the group to call police, but he left before officers arrived, Hines said.

About an hour later, Hines said, Anthony Rivera tracked Aviles-Rivera to a neighbor's house, where she was helping them unload gifts from the party. There, he allegedly shot Aviles-Rivera in front of neighbors, but she was able to run across the street to her house, with the ex-boyfriend in hot pursuit. That's when Hines heard screaming coming from inside the home and got up to go see what the ruckus was about. She said she saw Anthony Rivera walk out of the house, hop on his bicycle and ride away calmly.

"He came out like nothing happened," she said.

Hines said Aviles-Rivera was in her second-floor bedroom bleeding from the face, while the brother was lying on the first floor near the back door. She said both were conscious when medics arrived.

"[Police] probably could have saved her from getting shot if they had just looked for him," Hines said.

She estimated that Rivera and Aviles-Rivera had been dating for two years when they broke up. She described Aviles-Rivera as a sweet young lady.

"They're wonderful people," she said.

Hines' mother-in-law, Bernice Hines, lived in the home, which the siblings shared with their mother. She said Aviles-Rivera was trying to get her life together and had been living with Rivera before moving back in with her mother a few days ago.

"She wanted to go back to school and get her high-school diploma after she left nutbucket," Bernice Hines said, referring to the ex-boyfriend. "You can't leave nobody that's obsessed over you like that 'cause they won't allow you to live nowhere else 'cause in their mind she got somebody else.

"When they do something like that to a woman's face, they're trying to disfigure her so no other man will look at her," she added.

According to Joezer Quinones-Rivera's Facebook page, he is a Cavalry Scout for the Army and a 2011 graduate of Bodine High School. Bernice Hines said he is passionate about the military and loves making people laugh.

Anthony Rivera's Facebook page tells a different story. A status message in December said he and Aviles-Rivera were engaged, although her page makes no mention of it. And in June, he posted a picture of himself pointing two guns at the camera.

After friends warned him about the photo, he wrote: "Killers only exist because nobody cares about how angry they are until after they've taken a life. This picture represents how I've felt many times. I will not hide who I am for my environment made me this way. Thanks for your concern but fear not big bro . . . I'm a protector not a bully. This was just my warning to the bullies I'm up against lol."

Police stopped Anthony Rivera about 3:20 a.m. yesterday on Paul Street near Orthodox after they matched him to the description of the shooter. When the officer got out of his patrol car and ordered him to stop, police said, Rivera fled on to Frankford Avenue, where he pulled out a revolver and pointed it at the cop. The officer fired at him, but the chase continued on to Margaret Street, where he allegedly pointed the gun again at the cop.

At some point during the chase, police said, Rivera dropped his weapon, fell over a wall, and ran on to Salem Street and through a few back alleys before stopping. As the officer tried to handcuff him, he allegedly tried to punch the officer and a struggle ensued, during which, police said, Rivera reached for the cop's gun. The cop fired, striking Rivera in the back.

Lt. John Stanford, a police spokesman, would not confirm Anthony Rivera's identity or whether police had gotten calls about him in the hours before the shooting.

Stanford said the police-involved shooting is being investigated and will be reviewed by the District Attorney's Office. The officer involved has been placed on administrative duty, as is standard any time an officer discharges a weapon.