BELMONT -- A shooting on Highway 101 Sunday that left a Menlo Park man hospitalized was not a random act of violence, police said Monday.

But the reason for the nearly 12 shots fired from one vehicle into a red 2009 Dodge Charger in the southbound lanes of the freeway near the Ralston Avenue exit remains elusive, Belmont police Lt. Pat Halleran said.

Police aren't sure if the shooting was sparked by road rage or some other dispute between the three victims and the shooter.

Two victims -- a 19-year-old East Palo Alto man and 23-year-old Santa Cruz woman -- have been released from the hospital since gunfire and subsequent crash at about 3:30 p.m. Sunday. A 24-year-old Menlo Park man was still in the hospital due to his injuries.

The shooting led authorities to shut down all southbound lanes of Highway 101 for about an hour. But the investigation left some lanes blocked until about 7:30 p.m.

Halleran said the trouble between the two vehicles could have been going on since Highway 92, or about two and a half miles north of the shooting scene.

"There were cars everywhere," he said, adding police hope to locate videos drivers took of the incident. "Somebody had to see something."

Anyone with information or video can call the Belmont police at 650-595-7400.

Contact Joshua Melvin at 650-348-4335. Follow him at Twitter.com/melvinreport.