Police are looking for a man who shot and killed a 41-year-old father of seven after an argument on an MTA bus in the Bronx Monday afternoon.

The victim, identified by his family as Jonathan Pettigrew, was on a Bx36 bus near East Tremont Avenue and White Plains Road in Van Nest when he was shot in the abdomen by an unidentified assailant around 2:30 p.m., the NYPD said.

Officials said the two men had some sort of dispute that led to the gunfire, though it was unclear what they were arguing about. First responders took Pettigrew to Jacobi Hospital, where he was pronounced dead.

“ Right now it's just hard for me to believe what's going on because I'm really, like, in a state of shock,” said Avery Pettigrew, Jonathan Pettigrew’s older brother.

He told Gothamist that Jonathan Pettigrew was taking the bus from the restaurant where he worked to pick up his 4-year-old daughter from daycare. He wasn’t sure exactly what happened, but said he had seen news reports that a dispute started when Jonathan Pettigrew scolded the suspect for speaking too loudly on the phone. Police officials would not immediately confirm that version of events and said they were still investigating.

“ He got this anxiety where he, like me, we can't be around a lot of noise,” Avery Pettigrew said. “So, I guess the person that was on the phone was being very disrespectful and loud, and it was bothering him.”

The suspect, who police say was wearing a white shirt at the time, fled south on White Plains Road, officials said.

Avery Pettigrew said his brother was a hard worker who was just starting to move forward with his dreams of a rap career. He was a father to seven kids – though only the 4-year-old girl lived with him. He also said Jonathan was an avid sports fan, and had been planning to tune into Monday night’s Knicks game.

Shootings in transit are rare, especially on MTA buses. Last month, a stray bullet flew through a bus in East New York, Brooklyn, but no one was hurt. A 16-year-old boy was fatally shot while getting off a city bus in Queens last year.

NYPD data shows there have been four other murders in the city’s vast transit system through the end of May this year – up from one during the same period last year. Overall transit crime is down just slightly since last year, with grand larcenies making up the largest share of reported incidents.

Avery Pettigrew said the loss of his brother has rocked the tight-knit family.

“I keep crying, and when I cry I can't breathe,” he said.