A quarrel on a North Side street that allegedly ended with a Chicago city worker using a taxi to repeatedly run over and kill its driver apparently started over an $8 cab fare, authorities said Monday.

Police and prosecutors said Michael L. Jackson has not told them how such a common dispute allegedly escalated into an ugly incident in the Lakeview neighborhood, and Jackson now claims he was defending himself.

On Monday, his lawyers called the cabdriver, Haroon Paryani, 61, the aggressor, and said they agreed a fight was sparked by a disagreement over the fare.

After the quarrel became physical, Jackson, 37, a specialist in the city's Health Department, allegedly got into Paryani's cab and ran him over where Paryani had fallen face-first into the street. Prosecutors said a woman who witnessed the incident early Friday ran up and cradled Paryani's head, only to look up and see the taxi's backup lights on.

"She backed up to avoid being hit herself," Cook County Assistant State's Atty. Michelle Patsy said in a hearing Monday, where Jackson was ordered held without bail.

After the cab had come backward over Paryani, Patsy said, Jackson allegedly put the taxi in drive again. He then accelerated over Paryani a third time, she said, dragging him into the intersection of West Briar Place and Cambridge Avenue.

Joshua Rubin, who lives in the 500 block of West Briar, said he heard screaming and fighting outside his opened windows. Then, he heard someone shout "I am going to kill you!"

The noise prompted Rubin to see what was happening outside. But before he could reach the windows, he heard the screeching tires.

He said he immediately picked up the phone to call police. "I saw a body lying 10 feet behind the car," Rubin said.

Court records show Jackson lives in the 500 block of West Briar, near the scene.

Paryani, a married father of four, died of heart lacerations apparently caused by massive rib fractures, authorities said. Four people have been able to identify Jackson at the scene or leaving the cab on Broadway, authorities said.

Why Jackson, a longtime fundraiser for HIV-related causes, allegedly became so enraged was not immediately clear, as friends continued to describe him as a caring person with a good heart.

One of his lawyers, Michael Oppenheimer, acknowledged that the disagreement apparently started over the fare, which the meter showed was $8 when Jackson allegedly wrecked the taxi on Broadway.

But when Jackson is tried on charges of first-degree murder and aggravated vehicular hijacking, he apparently will claim self-defense during "mutual combat," and that Paryani was the aggressor.

"[Jackson] suffered a beating at the hands of the deceased," said Jon Erickson, another of his lawyers, who said Jackson received medical treatment Friday.

"He believed he was in danger of suffering further bodily harm."

Relatives of Jackson, including his mother, who were in court Monday after arriving in Chicago from Peoria, declined to comment.

The attorneys said they were not ready to discuss whether alcohol or drugs could have played a role, though Erickson said he was not aware of Jackson having a history of substance abuse.

Erickson said the picture prosecutors painted of Jackson going berserk is not how most who know Jackson describe him.

Erickson told Judge Raymond Myles that Jackson is a dedicated fundraiser, having pooled hundreds of thousands of dollars over the years for AIDS causes.

Jackson has worked for more than a year in the Chicago Public Health Department's sexually transmitted disease/HIV/AIDS division as a policy and communications specialist, officials said.

In 1992, Jackson established the Hearts Foundation, a non-profit organization that describes itself as supporting service groups for Chicago's gay and lesbian community.

A friend, Michael Bauer, a former Hearts Foundation board member, said the charges against Jackson came as a shock.

"It's unfathomable," he said outside Monday's bond hearing at the Cook County Criminal Courts Building.

Chicago Health Department spokesman Tim Hadac said Jackson was officially terminated from his city job Monday.

Before holding that post, Jackson worked as president of CaptiveCash, a division of the software and technology company Captive Customer, according to that company's Web site. Jackson, a certified public account with a bachelor's degree from Bradley University, headed a division that focused on connecting non-profit corporations and product companies.

Stan Sloan, executive director of Chicago House, which provides housing for people with HIV and AIDS, has known Jackson professionally for about seven years. He described him as a "friendly, mild-mannered guy." He said the incident was a horrible tragedy for both the victim's family and Jackson's.

Mujahid Ghazi, spokesman for the Paryani family, said he hopes justice is done in the Jackson case, pointing out that it is the second violent death of a Pakistani immigrant in as many years. A friend of Paryani, Mohammad Rafiq Haroon, 60, had his throat slashed during a 2003 robbery.

Paryani had worked for the Seven Day Cab Co. for about two years.

Paryani's family declined to comment Monday.

Prosecutors said after Jackson allegedly ran over Paryani the third time, he fled the area and crashed the cab on Broadway. There, he was confronted by another motorist, Patsy said, but he ran off.

Another witness, believing Jackson was in distress, then hailed him another cab.

Patsy said police became interested in Jackson after one of his lawyers contacted the city's corporation counsel, and that office called investigators. Jackson had turned himself in to police Friday.

Jackson is due back for a Feb. 24 hearing at the Criminal Courts Building.

Tribune staff reporter Tom Rybarczyk contributed to this report