Just before 6 p.m. Thursday, investigators said the shooter and another person inside his sedan struck another vehicle, causing it to spin out. Both suspects got out. One of them got people's attention.
"A Hispanic male, tan shirt, holding a really big gun, shooting at another car," reported a police dispatcher.
"One of the witnesses saw the weapon," HPD Assistant Chief Bobby Dobbins said. "He's familiar with guns and he believes it was an AR-15."
Police said as the victims' car rolled towards the gunman, he fired multiple rounds. Both men inside were killed.
According to police sources, a large trash bag with marijuana was in their car. Investigators are looking at all possible motives.
"Road rage? An accident? Narcotics? We don't know yet," Dobbins told reporters.
WATCH: HPD release details on shooting that killed 2 people during rush hour traffic on I-10E
HPD release details on shooting that killed 2 during rush hour traffic on I-10E
The suspects took off, leaving behind a crime scene on the freeway. Police do not have a good description of the suspects or their vehicle.
Several witnesses are being questioned. Investigators are urging anyone who may have seen or heard anything to call HPD.
"This is a scary event to happen at 6 o'clock at night on a busy freeway," Dobbins said.
Another driver, who carries a pistol in his vehicle for personal protection, feared for his life, police say, and fired at the shooter. They do not know if he was hit.
The victims have not been identified.