WATERTOWN, MA (WHDH/CNN) - A Massachusetts man is accused of stabbing a tow truck driver who hit and killed his mother.
Philip Horner is being held without bail.
The driver, 60-year-old Thomas Fogerty is in critical condition.
Cellphone video captures the graphic scene where witnesses said Horner jumped into the cab of Forgerty's flatbed tow truck and starts assaulting him.
The incident occurred after Forgerty’s truck struck Horner's 68-year-old mother yesterday.
She died at the scene.
The video then shows Horner falling out of the truck, stumbling before Fogerty gets out.
Seconds later, according to police, Horner pulled out a knife from his fanny pack and starts stabbing Fogerty in the side and back, even as Fogerty stumbles down the sidewalk.
Zeidan Tahaat shot the video.
"At the beginning, you know, I thought it's like, you know, just an argument between," Tahaat said. "And then, when I look at the wheel, you know, I saw the woman sneakers, you know, and then there's something, something real serious."
Horner pleaded not guilty even while his attorneys suggested to the judge the 38-year-old wasn't fit to be arraigned.
A court-appointed psychologist testified, however, that Horner has mental issues.
Prosecutors say they wanted him held without bail.
Horner's relatives left the courthouse without comment.
"Mr. Horner is being transported to a secure facility, where he'll be able to receive the medical attention that he needs," said Nick Louisa, his attorney.
Horner is charged with armed assault with the intent to murder.
He's undergoing a 20-day psychiatric evaluation before he returns to court.
Copyright 2018 WHDH via CNN. All rights reserved.