SAXONBURG — A borough man was arrested Wednesday on charges he doused his then-girlfriend’s 7-year-old son with flammable liquid.

The man’s own 15-year-old son then set the younger boy’s shirt on fire, Saxonburg police said.

Edward B. Myers, 35, allegedly used his cell phone to film the attack in May at his Carol Drive home as he watched the boy burn.

Myers, the 15-year-old and his 11-year-old son, that same day of the suspected torture, repeatedly shot the victim with airsoft guns and pellet-type guns, according to court documents.

The boy needed hospital treatment for third-degree burns on his face and chest, and welts on his forehead.

“I’ve seen a lot of horrible crimes against children during my career, but this one ranks among the worst of them,” said Saxonburg Police Chief Joe Beachem.

District Judge Lewis Stoughton arraigned Myers on felony assault and other charges. He is in the Butler County Prison on $250,000 bail.

The 15-year-old faces similar charges in county juvenile court, Beachem said.

Investigators are not sure what motivated the alleged sadistic attack, however, one of Myers’ sons reportedly claimed it was a “prank.”

But Beachem dismissed any claim that what happened was a prank.

“I’ve heard there was some animosity between Myers (and his sons) and the victim,” Beachem said, “but I don’t know what could motivate someone to do this.”

Police began investigating the case about 11 p.m. May 25 after speaking to Dr. Reginald Reginella, medical director at Butler Memorial Hospital.

Reginella told police that the hospital had treated the 7-year-old victim in the emergency room before he was taken to the UPMC Mercy Hospital Burn Unit in Pittsburgh.

The boy’s mother, who lives in Saxonburg, had driven him to Butler Memorial.

She told police that she had dropped off her son at Myers’ home about 2 p.m., and went shopping with a friend. She said Myers’ two sons also were there.

When she returned between 9 and 9:30 p.m. to pick up her son, she found him with burns to his chin, neck and chest.

Asked what happened, Myers claimed the injuries were accidental, she said.

“He stated he had been cleaning hair dye from the sink and had spilled nail polish remover on (the victim),” a police affidavit said.

Moments later and unintentionally, he told the boy’s mother that a lit cigarette fell on the boy’s shirt, igniting it, police said.

But the boy later disclosed to his father and to a social worker at Mercy Hospital that he had been “intentionally burned,” police said.

Police eventually interviewed the boy, who recounted that Myers and his two sons earlier that day had started shooting him with “some guns,” the affidavit said.

The guns fired “plastic balls or BBs,” police said, and hit the boy in his forehead.

He said Myers at some point threw something from the stove that hit him and started burning his eyes.

About that time, the boy said, Myers started filming the events that day with his cell phone camera.

The boy said he went into the bathroom to wash his burning eyes. But Myers followed and poured nail polish remover on him, documents said.

Soon after, the boy told police that Myers or one of his sons “did something and (the victim’s) shirt caught fire,” documents said.

Beachem said he suspects that it was the 15-year-old who lit the victim on fire.

When investigators eventually tried to speak with Myers to get his account of what happened, police said, “he stated we could speak to his attorney about that.”

Myers’ attorney was not immediately known.

Police later searched Myers’s home and recovered two airsoft guns and a pellet gun. They also found marijuana, documents said.

One of Myers’ cell phone still is being is being examined for evidence of the suspected attack on video.

Myers, who is unemployed and on disability, is charged with aggravated assault, attempted simple assault, reckless endangerment, and possession of a controlled substance and drug paraphernalia.