Alex Torres Santos is accused of killing brothers Jesus Perez-Salome, 8, Sebastian Perez-Salome, 9, and Joshua Lugo-Perez, 19, not pictured. (Photo of the Perez-Salome brothers from GoFundMe; Santos photo from the Lebanon County District Attorney’s Office)

Prosecutors in a Pennsylvania county said Friday they would seek the death penalty against a 22-year-old man who was on house arrest and wearing an ankle monitor for a previous shooting when he allegedly killed two young brothers innocently playing with kittens in their yard along with another young man in a senseless act of violence that also left a neighbor seriously wounded by gunfire.

Alex Torres Santos, 22, is accused of killing brothers Jesus Perez-Salome, 8, and Sebastian Perez-Salome, 9, as well as Joshua Lugo-Perez, 19, in Lebanon, Pennsylvania, on Tuesday, officials said. A 33-year-old neighbor was wounded by a stray bullet and was expected to recover, authorities said.

Santos and James Fernandez-Reyes, 16, face charges of three counts of criminal homicide, Lebanon County District Attorney Pier Hess Graf said. They also face aggravated assault, conspiracy and weapons offenses related to the shooting in Lebanon, a small city about 70 miles northwest of Philadelphia.

A third person was being sought in connection with the fatal shootings, officials said.

The district attorney’s office on Friday filed a notice of aggravating circumstances, statutorily mandated in cases where the prosecution intends to seek the death penalty, against Santos for his involvement in the triple homicide, Graf said.

The notice against Torres alleges five aggravating factors — multiple homicides, two victims under 12, and the grave risk to others posed by the defendant’s actions in a densely occupied city neighborhood, prosecutors said.

“In my 14 years as a Lebanon County prosecutor and in my nearly four years as the District Attorney, we have not filed a death penalty notice in any case,” Graf said. “No other murder committed during my time as the DA has risen to the specific legal standard necessary to seek death for the killer. This case meets that standard.”

She said the decision was not made lightly.

“There are some crimes – crimes like this one where young children were shot to death outside of their home as they innocently played with their kittens – that demand we charge accordingly,” she said.

The shootings devastated the family. The boys’ mother, who was working at a store nearby, heard gunshots and ran over to find them, said Felix Muniz Torres, the children’s uncle, in a phone interview with CBS News on Thursday from his home in Puerto Rico.

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

He described his nephews as “very innocent and polite,” always together playing, mostly with their superhero figures, the network reported.

“They were very close,” he said.

It all went down Tuesday night. Police were dispatched for a call of shots fired near 444 North Fifth Street in Lebanon City.

Police said at least 27 gunshots were fired from two guns.

Jesus Perez-Salome was found dead on his back porch, police said. Sebastian Perez-Salome and Lugo-Perez died at area hospitals.

Police found Lugo-Perez in the home, where it appeared he fled during the gunfire, police said. Authorities said the shooters targeted Lugo-Perez over “a previous argument” without elaborating, citing an ongoing investigation.

Lugo-Perez and the boys lived at the home. Lugo-Perez was not related to the boys.

Authorities said Santos and Fernandez-Reyes fled after the shooting and hid in a nearby home, but both were caught later. Police said a search turned multiple firearms, including an AR-15.

“The ammunition found in that firearm is visually consistent with ammunition utilized during the killings,” prosecutors said.

Santos provided both firearms, and both suspects fired rounds before fleeing with the murder weapons, authorities said.

Santos was out on bail for two incidents involving dangerous behavior with firearms, prosecutors said. Authorities said one case involved aggravated assault in which he brandished multiple handguns, fired, and struck a man multiple times.

In the second case, police alleged Santos illegally possessed a handgun without a license, possessed crack cocaine with intent to deliver, and illegally altered a handgun’s serial number.

The incidents occurred within two weeks of each other, authorities said.

Bail was initially set in the prior case for him at $100,000, but a judge lowered it to $50,000 over the prosecution’s objection, prosecutors said.

Under the conditions of the lowered bail amount that Santos posted, the suspect was required to wear a monitoring bracelet under house arrest, pending trial. He wore his bracelet to the homicide, thus serving as “no deterrent to a violent criminal willing to take a life,” Graf said.

“Tuesday evening, our community suffered another heartbreaking incident of gun violence,” she said. “Younger and younger defendants are picking up handguns and committing senseless shootings. Every homicide trial we undertake results in a first-degree conviction. Until the criminal appreciates the true outcome of the taking of a life – spending the rest of his own locked into a cell – nothing will change.”

The superintendent of the Lebanon School District, where the boys went, sent a letter to families on Wednesday.

“A young person’s death is always a heartbreaking and troubling event, and the loss of a young life can have a profound effect on the student’s friends and classmates,” the statement said. “It is important that we, as family members and educators, recognize this loss and offer assistance.

“We encourage you to be especially empathetic and prepared to offer support to your child during this time.”