Jacob D. Robida, 18, died at Cox-South Hospital in Springfield, Mo., hospital spokesman Randy Berger said.
Investigators said the high school dropout from New Bedford, Mass., had dabbled in Nazism, and police there said the attack that injured three men, one critically, at the Puzzles Lounge on Thursday was a hate crime.
New Bedford police said Sunday they were still trying to determine what motivated Robida and if he had any help.
"By no means is the investigation is over," said New Bedford police Capt. Richard Spirlet.
"I wish he would have lived and gone on trial," said Dan Sheterom, 51, who lives above Puzzles Lounge and frequents the tavern.
After the New Bedford attack, police say, Robida picked up 33-year-old Jennifer Rena Bailey at her home in Charleston, W.Va.
"Apparently she's had a prior relationship with this guy and had been corresponding with him. Other than that, we're still in the dark about that," West Virginia State Police Sgt. C.J. Ellyson said Sunday.
"The extent of their relationship I don't know," he said, adding that investigators also didn't yet know how they met.