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The assault occurred about 12:30 p.m., as the assailant and victim were approaching a transit depot on Taylor Street, according to San Diego police. When the trolley pulled to a stop at the station, the attacker jumped off and ran away, SDPD Detective Gary Hassen said.

Medics took the victim to a hospital for treatment of a wound of undetermined severity.

Beau Butler, who didn't see the actual stabbing, told 10News the suspected assailant was standing next to her on the trolley.

"We were just enjoying the train ride and that's when he just randomly came up and stabbed this gentleman," Butler said. "That gentleman was bleeding and we were just trying to make sure we guarded him and we all kind of stuck together."

One passenger is said to have taken off his shirt to put around the victim's neck.

Fear mounted as passengers said they were trapped on the trolley.

"A bunch of people were hitting the red button to stop the train," Butler added. "The train just kept going. We were all just kind of panicking."

Butler said the suspect remained in a corner.

"He was just twitching," Butler said. "The side of his face was drooping. I will never forget what he looked like."

The assailant, meanwhile, confronted a motorist near Perry's Cafe on Pacific Highway, punched him in the chest, forced him out of his white 1992 Buick sedan and drove off to the north, the detective said.

Witnesses described him as a roughly 6-foot-1, 230-pound man in his 40s, wearing black pants and a black jacket.

Shortly before 3 p.m., a television news cameraman driving through Clairemont Mesa spotted the stolen Buick parked and abandoned alongside the southbound lanes of Interstate 805, near Mesa College Drive, Hassen said.

Officers with a service dog searched a brushy open area into which the carjacker apparently had fled after pulling over on the freeway, according to Hassen. About 4 p.m., police took the suspect into custody off the 7800 block of Mission Center Road.

His name was not immediately available.