FLINT, Mich. (AP) — Investigators say a knife-wielding serial killer has been attacking men on Flint-area streets since May, killing five people and wounding eight others in a vicious spate of violence that may be motivated by racial hatred.

Survivors have described their assailant as a muscular, young white man, and all but one of the 13 victims was black, Flint police Lt. T.P. Johnson told The Associated Press on Friday. Flint is a predominantly black city, and investigators are unsure if the suspect was targeting blacks or whether the victims were chosen at random.

The victims were all outside alone at night. Survivors have said the attacker approached them under the pretense of needing directions or help with a broken down vehicle.

“He then pulls a knife and attacks them without saying anything more,” Johnson said.

“A knife is a very personal weapon. To stab somebody repeatedly, there has to be some rage going on,” he said.

WATCH COVERAGE OF THE SERIAL STABBINGS HERE

Detectives have been investigating the attacks since they started, but a pattern only became apparent on Tuesday, the day after 49-year-old Arnold Minor was found slain along a Flint street, Johnson said.

Flint is the birthplace of General Motors and was once a powerful auto manufacturing town, but its economy and population have steadily declined over the past few decades and have led to cuts in police and fire protection.

Mayor Dayne Walling on Friday urged residents to watch out for each other and to remain vigilant.

“You have somebody in your life who is vulnerable, look out for them,” he said.

Bob Katrinic, a 59-year-old white man from Burton who runs a leather goods business, spoke to a reporter Friday afternoon only a few feet from where Minor was killed. Katrinic said he’s taking precautions.

“When I go to work, I know I’m going to be packing,” said Katrinic.

Alexandria Sullivan, 20, a black criminal justice student at Mott Community College, said she tells her brothers to avoid situations that might lead to trouble. Flint has had problems with violence between young black men.

Now, with older black men the apparent targets, Sullivan said the same kind of common sense should apply to them.

“Walking at night alone? At four in the morning? By yourself? Why would you do that?” she said. “People are saying, ‘Oh my God, it’s a serial killer,’” Sullivan said.

Michigan State Police are leading a task force investigating the attacks. Ten have been in Flint, about 50 miles northwest of Detroit. Three others were in nearby communities.

On July 30, the body of 60-year-old Frank Kellybrew was found not far from the Flint Township motel he had called home for about 10 months.

The manager of Hometown Inn said Kellybrew had walked to the other side of Interstate 75 to buy some things from a gas station. The next morning his body was found by sanitation workers corralling trash barrels near a restaurant.

Kellybrew didn’t stand out any more than the other tenants at the motel, which rents quite a few rooms on a month-to-month basis, manager John Henson said Friday.

He liked watching television in the motel lobby or having a cup or two of coffee.

“He was a nice guy; kept to himself,” Henson said. “If he didn’t know you, he would just avoid you and have nothing to do with you.”

In his short time at the inn, Kellybrew enjoyed walking over at night, after business hours, to the restaurant near the freeway.

“He would sit on the bench at night,” Henson said. “He’d just go over there, and sit and relax. It’s pretty quiet over here at night when everything closes.”

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Associated Press Writer Corey Williams in Detroit contributed to this report.

Copyright 2010 The Associated Press.