The deadly argument began with an unexpected visitor.

After Mark Quadrel, 58, arrived unannounced at his son's Norristown apartment on Wednesday afternoon, father and son got into an argument, the son would later tell authorities. It was not clear what caused the confrontation, police said, but it enraged Steven Mark Quadrel so much that he went to his truck, grabbed his 9mm Beretta semi-automatic pistol, and returned to his Airy Street apartment to ambush his father, shooting him dozens of times in the back and the head.

Quadrel then took off on foot, shooting at a 12-year-old boy on a scooter as he ran down nearby Sandy Street, according to court documents.

On Thursday, Quadrel was charged with first-degree murder, aggravated assault, and related crimes. The 24-year-old told police he shot his father after a conversation became heated. Quadrel said he shot once at the boy on the street because he was "creeped" out by the sight of him, according to court documents. No attorney for Quadrel was listed on court documents as of Friday.

Police arrived on the 600 block of Sandy about 4 p.m. Wednesday, responding to a call about shots fired. Authorities said they found Quadrel on the street. He struggled with officers as he was arrested, and they soon located his pistol on the ground nearby.

Quadrel asked officers repeatedly whether his father was "OK" and urged them to check on him. But he also told the officers over and over again that he had killed the man, according to the documents.

Later that night, as officers looked for Quadrel's father and investigated the shooting, they returned to Quadrel's apartment on the 600 block of East Airy Street. Inside, they found Mark Quadrel face down on the floor. He was dead, having been shot at about 30 times and struck repeatedly.

The 12-year-old who had been shot at on the street suffered a graze wound to a hand and arm. He was treated at Einstein Medical Center. The boy told authorities had been riding his scooter down the street with two friends when Quadrel ran past him and then back toward him. Quadrel pointed the gun at the child — its red laser lighting up on on the boy's face. He lowered the weapon and then fired, authorities said.

Quadrel is being held without bail at the Montgomery County Correctional Facility. He awaits a preliminary hearing scheduled for Nov. 9.