A man wearing a bulletproof vest died after he was shot in the chest by a friend at a party.
His girlfriend, Mary Warstler, told the ABC13 news channel that the 39-year-old did not think the gun was loaded and had not meant to kill his friend.
Although she had not attended the party, she said she spoke to her boyfriend shortly after he fled the scene of the shooting. He later turned himself in.
She said he told her that he had gone to "sell his friend a flak jacket." The victim, she said, had told him to "shoot me" after he tried it on.
“It’s so bad because he didn’t know the gun was loaded,” she added. “He felt bad for what happened to his friend.”
She added that Mr Griffin had tried to save his friend before fleeing the scene and later became suicidal. He subsequently suffered two seizures and was taken to hospital.
Homicide Sgt Mark Holbrook confirmed part of the story.
"The victim put on a bulletproof vest and another man who has a gun winds up shooting him," he said. "It's unusual, but these things happen sometimes."
The victim was dead by the time officers arrived at the scene, he added.
He also confirmed that Mr Griffin was taken into custody on Sunday afternoon after being treated in hospital.
Along with manslaughter, Mr Griffin had also been charged with unlawful possession of body armour and being a felon in possession of a weapon.
Just over 3,200 people were killed by a firearm in Texas in 2015, according to the US Centre for Disease Control and Prevention, a rate of 11.7 per 100,000 population.
The rate nationwide in 2015 was 11.1 per 100,000.