The party bus, which was chartered out of Compton, was carrying approximately 40 to 50 people and had several planned stops in Hollywood.
The bus made a pit stop in front of a strip mall on Sunset Boulevard so some of the passengers could get out and use the bathroom shortly before midnight.
That's when a fright broke out. The altercation turned deadly when someone pulled a gun and started shooting. Two people, both men in their 20s, were struck by bullets. One was pronounced dead at an area hospital, and the other was listed in critical condition.
Detectives say they're still trying to figure out exactly who was involved in the fight.
"It's not clear if the fight was among occupants, all of whom were on the bus, or if it was between the occupants on the bus and passersby," said LAPD Capt. Peter Zarconi. "There are two people in custody that were involved. We haven't determined for certain that they were on the bus or not."
Police say this was a gang-related shooting. The two people in custody have not been officially charged, though investigators believe one of them is the gunman.
Witnesses say when gunfire rang out, things turned chaotic.
"It was just crazy. I mean, people running everywhere. After the incident occurred, about 25 minutes later, one of the shooters came up from one of the side streets, a lot of the victims who were on the bus noticed him, and he did get apprehended by officers," said John Wilson, a witness.
Police say there was alcohol found on the bus. Investigators are looking at surveillance footage from inside the bus and from area businesses to piece together exactly what took place.
A stretch of Sunset Boulevard between Gower Street and El Centro Avenue was shut for police investigation. All roads have since reopened.