DETROIT (AP) _ A man irate over a fender-bender viciously beat the woman whose car he bumped and threatened to ``knock (her) brains out,'' terrorizing her into a fatal jump into the Detroit River, a prosecutor said Tuesday.

Martell Welch Jr., 20, is charged with murder in the Aug. 19 drowning of Deletha Word. Witnesses say he attacked the much smaller woman after their cars collided on the Belle Isle park in the Detroit River.

``As Martell Welch comes toward her with his arm upraised, she goes into the river,'' prosecutor Kevin Simowski said in opening statements.

The death drew national attention when initial accounts said onlookers cheered the attack. Police later said most witnesses were too shocked to do anything as the 6-foot-1, 290-pound Welch attacked the 4-foot-11, 115-pound woman.

Welch's lawyer admitted his client was wrong to attack the 33-year-old woman, but said he didn't cause her death. Wanda R. Cal said the drug PCP found in Word's body explained her jump into the river.

``It was either an accident or suicide,'' Cal said.

Simowski said it was Welch who caused the initial fender-bender by backing into Word's car at about 2 a.m. on Belle Isle. The woman drove away with Welch in pursuit, honking his horn and flashing his lights.

The cars collided twice as traffic slowed near the bridge off the island, Simowski said. When Word's car stalled, Welch ran to it and started beating her, intending to kill or seriously injure her, he said.

Welch pulled her out, ripped off her shirt and banged her head on his car. Some of Welch's companions at first joined the attack but then tried to stop him, Simowski said.

``His buddies said basically, `That's enough. Chill out,''' he said.

But Welch threw Word over a barrier between the road and a pedestrian walkway, then came after her with the tire iron, saying, ``Bitch, I'm going to knock your brains out,'' Simowski said.

As a companion cut off the woman's escape, she climbed over a railing and jumped when Welch neared her, he said.

A witness later described seeing Welch approach the half-naked woman with ``his arms ... raised in the air.'' Tiffany Alexander of Detroit said Word let go of the railing and fell as Welch got within five feet of her.

The victim's mother, Dortha Word, also testified Tuesday in tears, describing how she saw her daughter the evening before her death and later had to identify her body at the morgue.