Weir was scheduled for surgery today to repair damage to the right side of his face, Detective William Rourke said.
A warrant charging Weir with first-degree murder has been issued, police said.
The shooting took place at about 12:50 a.m. in the 200 block of North Locust Street, a block from Vinzant's 332 N. Locust St. home.
The initial investigation indicated Vinzant and Weir, who formerly had lived together, had been involved in a fight Tuesday night at the Neighborhood Inn on North Mulberry Street, Detective Carroll Braun said.
"They were fighting there, verbally and physically," Braun said. "She left with a man who was going to walk her home because she was scared of going alone."
Weir left at the same time, and caught up with Vinzant, Braun said.
Family members were struggling Wednesday to make sense of the shooting that claimed the life of Vinzant, the mother of three children, including a son by Weir.
"It wasn't alcohol, it was his temper," said Betty Jordan, Vinzant's mother.
Jordan, who lives a block from her daughter's home, said she got home from her security guard job at midnight and went to bed.
"My other daughter's boyfriend came up and said I'd better come," Jordan said. "I just knew."
"She did everything she could," Jordan said, noting that Vinzant had made Weir move out about a month ago.
"Before, I'd ask her why she didn't leave him and she'd say, 'But Mom, I love him,'" Jordan said.
She said Vinzant and her 15-year-old daughter had pressed second-degree assault charges against Weir for an earlier incident.
"I think he was afraid of that upcoming court date," Jordan said.
The Washington County state's attorney's office confirmed that Weir was scheduled for trial on Sept. 23 in District Court on charges of assault against Vinzant and her daughter.
Linked by their young son, Weir and Vinzant would see each other when he came to visit the child, Jordan said.
"I told John to come to my house and I'd get the child ... so there wouldn't be any trouble," Jordan said.
Neighbor Ann Collins said her husband woke her when he saw the police floodlights in the street outside their home at 246 N. Locust St. shortly after the shooting.
"Weir's truck was parked right in the middle of the intersection when I looked out," Collins said.
The police found a shotgun at the scene.
Vinzant's two older children and the 2-year-old child she had with Weir were being cared for by family members, including Vinzant's younger sister, Donna Wilson.
Wilson and her boyfriend, Todd Guessford, had moved in with Vinzant about a month ago to help her with the children, Jordan said.
Wednesday's homicide was the second in Hagerstown and the third in Washington County in 1998.
The unsolved stabbing death of Clara Elizabeth Miller, whose decomposed body was found off Burhans Boulevard last March, was the first, according to Lt. Margaret Kline.
On Feb. 5, Washington County sheriff's deputies investigated the death of Samuel Wolfe at his Williamsport home. Robert Ray Eckard, 21, of Marlowe, W.Va., is awaiting trial in that case.
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