The officer from Burlington County is now facing second-degree murder charges.
On a ramp near Interstate 97 in Millersville, Maryland, police say off duty law enforcement officer 40-year-old Joseph Walker opened fire killing a man.
Walker is a detective for the Hudson County Prosecutor's Office in North Jersey but he lives on Cambridge Court in Eastampton, Burlington County.
Many of his neighbors know him well.
"Not Joe, anybody but Joe. It's just something that you would never see in him. It's hard to believe it, it's just shocking," said Wayne Stevenson, neighbor.
Walker was in a minivan with his wife and three small children in Anne Arundel County around 8:30 Saturday night.
Investigators say Walker followed the other driver, 36-year-old Joseph Harvey of Halethorpe, Maryland. Both men pulled over and the victim jumped out.
State police say Harvey reportedly approached Walker's van in an aggressive manner, prompting Walker to shout out that he was a police officer, before firing his 45 glock.
Harvey was struck and killed.
"I spent 22 years in corrections so I'm not surprised at human behavior so it could happen. It happens to the best of people, happens to the worst of people," said Ron Brown, neighbor.
"The guy has a great outlook, very professional, very friendly. I mean, as a professional, the man seems as if he knows his job, I mean he knows the law ," said Tom Mills, friend.
The stress of the incident apparently caused Walker to have chest pains.
He was checked out at the hospital before troopers hauled him off to jail and charged him with second degree murder and manslaughter.
"If you stop and pull over, you're not going to talk. You know something is going to happen and it's not going to be nice so road rage - let it go, keep moving," said Mills.
Neighbors say Officer Walker has been with the Hudson County Prosecutor's Office for as long as they've known him and he's lived on their street for about five years.
He is being held on $1 million bail.