Axel Barreto, 30, was arrested late Wednesday night after a tip call led police to the Knights Inn in Bensalem, Bucks County. Police say he was in the company of a female neighbor.
Police say Barreto was more concerned that his wife would find out about the liaison than he was about the arrest.
Barreto was not armed, police say, and he was arrested without incident.
On Thursday police said Barreto, who is now charged with three counts of murder, is cooperating.
Barreto was arraigned Thursday night and is being held without bail.
"He's a bad guy. He's got a long history of violence, drug dealing in his past and we're happy to get him off the streets," said Capt. James Clark of the Philadelphia Police.
Barreto is accused of shooting at a car full of seven teenagers on East Luzerne Street around 10:30 p.m. Tuesday in Juniata Park. Javier Orlandi and Joshua Soto, both 14, were killed right away.
The family of a third victim, 14-year-old Dante Lugo, took the boy off life support on Wednesday night.
A 16-year-old driver was shot in the neck and hospitalized. He has since been released.
Investigators say the boys and Barreto's stepsons had been in an ongoing conflict at school and on Facebook.
"It just appears it was senseless back-and-forth, teenage bullying," said Capt. Clark.
The murdered Orlandi was a young man who had been in a number of foster homes and had some brushes with the law. However, grieving officials at his former middle school say he showed great academic potential and leadership ability.
"He had a light. He had a spark and it was despite the worst of circumstances at times, that he didn't have asked to be placed on him," said teacher Stephanie Andrewlevich.
When asked why the boys were out late on a school night, apparently riding toward a violent confrontation, assistant principal Erica Green said 'peer pressure.'
"We've all fallen for it. It happens and we all need someone in our corner that says 'I believe in you, you can do it, come home tonight," said Green.
Police believe the victims were lured to the area on the promise that there would be a street fight, but instead they were ambushed.
Police say as Barreto approached the car the teens pulled away and drove around to the back of the house. Barreto then allegedly went to the back of the home and opened fire on the car, unloading ten to twelve rounds at point-blank range.
The 16-year-old was able to drive the car to St. Christopher's Hospital.