Prosecutors in Pennsylvania are seeking the death penalty against one of the suspects accused of fatally shooting two brothers, ages 8 and 9, as they played with kittens in their backyard earlier this week.

A teenager who also lived at the property was slain in the shooting and was the apparent primary target, police said.

Sebastian Perez-Salome, 9, Jesus Perez-Salome, 8, were outside their home in Lebanon, a city of about 144,000 residents 70 miles northwest of Philadelphia, on Tuesday night at about 10 p.m. with the kittens when the shooting erupted.

Officials said the third person killed, 19-year-old Joshua Lugo-Perez, was believed to be the target over what authorities called a “previous argument.” He was not related to the two children but lived in the same house.

A 33-year-old man who lives next door was also injured when he was hit by a stray bullet.

Alex Torres Santos, 22, and a 16-year-old male were arrested and charged with three counts of criminal homicide. Authorities said a third suspect is still being sought.

Lebanon County District Attorney Pier Hess Graf said Friday she will seek the death penalty against Torres-Santos for the triple homicide due to “aggravating factors” she hasn’t seen in her 14 years as a prosecutor and four years as district attorney.

“No other murder committed during my time as the D.A. has risen to the specific legal standard necessary to seek death for the killer,” Graf said in a news release. “This case meets that standard.”

Boys killed were ‘innocent and polite,’ family says

The children’s mother was at her job at a convenience store near the house when she heard gunshots, according to their uncle, Felix Muniz Torres.

Muniz Torres told the Associated Press in a phone interview from his home in Puerto Rico that the mother raced home and found them shot. Her other child, 13, was fortunately away at a school event at the time of the shooting, he said.

“She’s in shock and is unable to speak coherently,” Muniz Torres said.

Jesus Perez-Salome was pronounced dead at the scene. Sebastian Perez-Salome and Lugo-Perez both died a short time later at hospitals.

The boys were “innocent and polite,” Muniz Torres said.

“They were very close,” he said, and always played together, usually with superhero figures.