The 25-year-old man apparently stormed the stage of the Columbus (Ohio) nightclub minutes into the performance late on Monday, firing repeatedly at Darrell "Dimebag" Abbott from close range, before turning his gun on another band member of the rock group Damageplan.
In the ensuing melee, Nathan Gale apparently was able to reload his handgun and fire randomly into the packed Ohio nightclub, killing two more people and injuring two others.
Police would not confirm reports that one of the other fatalities was Abbott's brother, Vincent Abbott.
Some of the 250 fans packed into the club initially thought the rampage was staged, but quickly scattered and stampeded for the exits as Abbott fell to the ground in a pool of blood, according to witnesses and police.
"It was just chaos," fan Steph Elias told the Columbus Dispatch. "We didn't know if it was part of the show. We didn't know what was going on at all. Everybody was standing there like a deer caught in the headlights."
"It was just chaos. We didn't know if it was part of the show. We didn't know what was going on at all. Everybody was standing there like a deer caught in the headlights"
A police officer patrolling the area near the Alrosa Villa club arrived on the scene minutes after panicked fans alerted authorities to the rampage, to find Nathan Gale holding a hostage in a headlock and still shooting.
"It appeared that he was about to kill this hostage when the officer basically put an end to it," said Sergeant Brent Mull, a spokesman for the Columbus police department.
Mull said there was no obvious motive for the shooting.
"We may never know the motive for this. Unless he left a note or there is something he left somewhere else, we may never know the motive," he said.
Mull did, however, confirm reports that witnesses had heard someone, possibly Gale, screaming about the break-up of the '90s metal group Pantera, which was founded by Abbott and his brother Vincent Abbott.
The band's 1994 album, Far Beyond Driven, hit Billboard's number one slot.
The Grammy-nominated group disbanded in 2002 and the two Abbott brothers went on to found Damageplan, which released its debut album, New Found Power, this year.
The group was reportedly on a nationwide tour, performing in Buffalo, New York on Tuesday, with a scheduled stop in Flint, Michigan, on Thursday.
Web chat rooms were buzzing with the news on Tuesday, with fans expressing their shock and disgust at the death of Dimebag Darrell, one of contemporary heavy metal's most influential guitarists.
"This is the biggest death in metal since Cliff Burton died in 1986, both of which occurred while on tour. While Cliff died in a tragic bus accident, Dimebag was shot on stage, the one place where you're supposed to be safe," read one posting on a VH1 website.
Authorities named two of the four fatalities as Erin Halk, 29, and Nathan Bray, 23.