Philadelphia police officers fatally shot a 12-year-old boy in his back in South Philadelphia last week after a bullet was fired into the officers’ vehicle, officials have said. The boy, Thomas Siderio, was pronounced dead minutes after the shooting. On Tuesday, Police Commissioner Danielle Outlaw announced that the officer who fatally shot TJ will be fired.

Here is what we know, and don’t, so far.

» READ MORE: The Philly officer who fatally shot a 12-year-old boy will be fired, Commissioner Danielle Outlaw said

What do police say happened?

According to a police statement released last week, four plainclothes officers were stationed in an unmarked car at 18th and Johnston Streets at 7:24 p.m. on Tuesday, conducting an ongoing gun investigation.

There, they spotted two people —12-year-old TJ and an unidentified 17-year-old — standing less than a block away at 18th and Barbara streets. According to the police statement, officers recognized the 17-year-old as someone wanted for questioning in their firearms investigation. Police said officers approached the pair because they believed one of them had handgun, and drove toward them in the unmarked car.

According to the police statement, officers stopped a few feet north of Barbara Street before turning on the red and blue emergency lights on their unmarked vehicle.

That’s when police said they heard gunfire and glass shattering in the car’s rear passenger window. Shards of glass struck one of the officers sitting in the back seat.

(Later, police determined that the bullet came through the rear passenger window, striking the inner doorframe of the police car, tearing through the passenger seat headrest, and lodging in the car’s headliner.)

According to the police statement, two other plainclothes officers exited the unmarked vehicle, firing a total of four shots at the 12-year-old boy — who police said was holding a gun — as he ran away on the sidewalk of Barbara Street. TJ fired one shot at the car, police said during a press conference Tuesday.

One of the officers pursuing TJ fired twice, striking the boy in his upper right back area once, according to the police statement. The bullet exited TJ’s body from the left chest area, police said.

The boy was taken to Penn Presbyterian Medical Center and pronounced dead at 7:29 p.m., according to the police statement.

“It’s just a sickening and saddening situation all around,” Outlaw said Tuesday. “By the grace of God, officers were not shot and killed or not shot in the head ... It is tragic that a 12-year-old had access to a gun. It’s tragic that we have trigger-pullers as young as 12. It’s tragic the circumstances that even lead our young people out there in the first place. And it’s tragic that we had one of our own again, go against everything who we say we are.”

Outlaw said Tuesday that it’s “not uncommon” for plainclothes officers to be out on the street, but that their operation is being revisited via an ongoing administration investigation.

“This incident does not reflect who we are as the Philadelphia Police Department,” Outlaw said. “It is not aligned with our values of honesty, honor, integrity, and service.”

» READ MORE: Philadelphia police fatally shot a 12-year-old in the back after their car was hit by bullet, officials say

What have others said happened?

The mother of the 17-year-old at the scene told The Inquirer her son’s account of the shooting differs from the police description. She said that according to her son, officers did not turn on their emergency lights before the gunshot rang out.

She said that her son and TJ saw the unmarked, black Chevrolet Cruz circling the block prior to the shooting. When the car stopped, she said the pair ran, afraid someone inside was looking to attack them and not knowing there were police officers inside.

On Tuesday, Outlaw said that the department has received “additional evidence that corroborates that the officers did in fact activate their emergency lights prior to being fired upon.”

» READ MORE: Mystery deepens on whether 12-year-old boy was armed when police shot him in the back

Who was Thomas “TJ” Siderio?

TJ was a seventh grader at George W. Sharswood Elementary School in South Philadelphia. A friend who knew TJ from the neighborhood said the boy had a turbulent childhood but “always tried to put a smile on everybody’s face.” He told The Inquirer he saw the boy and the 17-year-old just before the shooting, and that the pair said they were on their way to hang out at the nearby Barry Playground.

TJ is the youngest person to have been fatally shot by a Philadelphia police officer in decades.

Did TJ Siderio have a gun?

Police said TJ was holding a stolen Taurus, 9MM semi-automatic handgun, equipped with a laser. Police said the gun was loaded with one round in the chamber and five rounds in the magazine.

Police sources have said during the first two shots officers fired at the boy, he was holding a gun. But the last two shots — one of which was fatal — are “concerning,” the sources said, because TJ may have tossed his weapon before he was hit.

Is there body camera footage of the shooting?

The plainclothes police officers were not equipped with body-worn cameras during the shooting, said Deputy Commissioner Benjamin Naish, who oversees investigations. Naish said last week that police are trying to recover surveillance footage from the area.

Home surveillance footage provided to The Inquirer by residents and motion-activated in the aftermath of the shooting, shows TJ on the ground about a block east of where police said they first saw him.

Just after 7:20 p.m., an officer appears on the surveillance video holding his face and asking, “Am I shot?”

“No, you’re not shot,” another officer replied.

When a resident asked the injured officer if he wanted a wet paper towel, he replied: “I’m fine.”

Then, another neighbor can be heard asking police: “Could you tell me what happened? They killed him right in front of my house.”

City officials denied a request to provide surveillance footage from cameras installed at a nearby city-operated playground, citing the ongoing investigation.

What happened to the injured police officer?

The officer was struck in the face by shards of glass, treated at Penn Presbyterian Medical Center, and released.

Who is the police officer who shot TJ Siderio?

The Philadelphia Police Department has declined to identify the officer, citing potential threats to his safety. But police sources with direct knowledge of the investigation said the officer was Edsaul Mendoza, a five-year veteran assigned to a task force in South Philadelphia.

Philadelphia Police Department policy typically allows officials to release the names of officers who shoot people within 72 hours, but the department has declined to release all officer names in this instance until police “conclude that the discharging officers no longer have a credible threat against them,” Outlaw said during Tuesday’s press conference.

» READ MORE: Philly police decline to identify officers in killing of 12-year-old, citing threats

The officer who fatally shot TJ will be suspended Friday with intent to dismiss, per the department’s collective bargaining agreement with the police union, Outlaw said Tuesday. Outlaw said that based on “a variety of evidence” she had reviewed, it was “clear” that the officer had violated the use of force policy.

“All use of force has to be proportionate to the resistance they’re trying to overcome. I will also tell you that our policy clearly states that excessive force will not be tolerated,” Outlaw told reporters Tuesday.

» READ MORE: The Philly officer who fatally shot a 12-year-old boy will be fired, Commissioner Danielle Outlaw said

The four officers who were in the unmarked car at the time of the incident — Officers Mendoza, Kwaku Sarpong, Alexander Camacho, and Robert Cucinelli — were detailed to an investigative team. The officers have all been on the force for fewer than six years, according to city payroll records. All officers involved were placed on administrative leave pending the outcome of the investigation, a city spokesperson said.

Police said last week that the boy fired a gunshot into the police vehicle, then two officers got out and fired shots toward TJ.

Police records indicate that Camacho was the officer who was injured by shards of glass.

Did TJ Siderio fire a shot at police?

Police say he did. In a statement last week, Police Commissioner Danielle Outlaw said “a young child with a gun in their hand purposely fired a weapon at our officers.”

The ballistic evidence was recovered or is in the process of being recovered, Naish said during a virtual briefing last week. “I can’t be definitive about exactly everything at this point,” he told reporters. “But I can be definitive that a shot was fired into the police vehicle and the gun was recovered.”

Five spent shell casings were found at the scene.

Were the police lights flashing on the unmarked car at the time of the shooting?

Police said they were, but that account has not yet been verified through video footage.

Why did officers shoot TJ Siderio in the back?

During last week’s briefing, Naish said that “it’s too early to speculate” and that police don’t yet have a “definitive determination” of what happened.

“While indications from the medical examiner is that the bullet entered into [TJ’s] back, that doesn’t mean that he was fleeing and that there was not a gun being pointed towards or in the vicinity of the officer,” Naish said, adding that police believe the boy was holding the handgun when officers shot him. “The angle of the projectile entering the young man is indicative that he was not fired [on] directly behind him. But his body could have been turning.”

“That doesn’t mean that he wasn’t continuing to be a threat to the officers,” Naish said.

The statement issued by police last week said TJ “fled on foot east on the north sidewalk.”

What are the laws around police officers using deadly force?

In 1986, the U.S. Supreme Court ruled that it was “constitutionally unreasonable” for police officers to use deadly force to stop a suspect who had committed a felony from fleeing.

But in Pennsylvania, the law states that officers are justified in using deadly force if a suspect “has committed or attempted a forcible felony, or is attempting to escape and possesses a deadly weapon.” The Philadelphia District Attorney’s Office has argued the state Supreme Court should declare that part of the law unconstitutional.

A 2015 Philadelphia directive notes that an officer is not justified in using deadly force only if a suspect resisted arrest or attempted escape, and that other factors should be taken into consideration.

Another directive, implemented in 2021, forbids officers from shooting at a fleeing suspect “who presents no immediate threat of death or serious bodily injury.”

» READ MORE: The police shooting of Thomas Siderio could renew debate over use of force laws

What happened to the 17-year-old at the scene?

The other person on scene — a 17-year-old who has not been identified but who police say was wanted for questioning in the gun investigation — was briefly detained and then released.

Staff writer Anna Orso contributed to this article.