CHICAGO (AP) _ John Costalupes, once a promising medical researcher with sterling academic credentials, ended up a drifter obsessed with revenge.

Living in a beat-up car littered with food wrappers, garbage, a few clothes and his typewriter, the 45-year-old bachelor nursed a grudge against his former boss, Professor Mario Ruggero.

``It really is only a matter of time until violence and probably even bloodshed finds its way to the University of Minnesota,'' he wrote in an ominous Nov. 20 letter to Dr. William Brody, the school's provost for health sciences.

He made good on his threat less than four months later.

On March 9, Costalupes shot Ruggero at Northwestern University in Evanston, Ill., shouting ``You ruined my life'' as he wounded him in the wrist, pelvis and leg. A day later, Costalupes killed himself on the Minnesota medical school campus after trying to barge into the dean's office.

``He was probably very intelligent, but obsessed,'' said Joy Rikala, the University of Minnesota's police chief.

Costalupes was educated at some of the nation's most distinguished universities: the University of California at Berkeley, Johns Hopkins, and Stanford, where he received a doctorate in neurosciences.

But he began emitting danger signals at least 10 years ago.

He resigned in 1984 from Johns Hopkins, where he was doing lab work and post-doctoral studies, rather than face disciplinary proceedings for allegedly erasing scientific data from a magnetic tape.

One of his superiors at the time, Professor Murray Sachs, said even though Costalupes was a ``very capable researcher,'' he tried to warn Ruggero against hiring him.

``I was under constraint (about what I could say), but I said `See the university attorneys,''' Sachs recalls telling Ruggero. ``But he asked again if I could tell him anything about Costalupes and I said, `Mario, you're not hearing me, you have to call the university attorneys.'''

``He didn't do that,'' Sachs said. ``He didn't follow up.''

Ruggero, then a prominent professor of hearing sciences at the University of Minnesota, hired Costalupes in 1985 for a two-year research project. It took about a year for their relationship to sour.

``Your overall performance in my laboratory has been unsatisfactory,'' Ruggero wrote in a letter, saying Costalupes had been unwilling to carry out assignments. ``Continued unsatisfactory performance would be sufficient grounds for your dismissal.''

The two had a shouting match, and Ruggero eventually changed the locks on his laboratory and assigned Costalupes elsewhere.

After the two men settled a grievance in which Ruggero was accused of breach of contract and unfair treatment, Costalupes left the university in May 1987. After that, he lived off temporary work and an inheritance.

``He lived in some apartments for very short times, most recently in motels and very recently in his car,'' Rikala said.

And his anger continued to smolder.

He tracked down Ruggero, who had taken a job at Northwestern, and shot him in a university parking lot. Police said Costalupes thought Ruggero stole his work at the University of Minnesota and got him fired. Associates deny Ruggero was a plagiarist.

Costalupes' resentment was evident in letters and documents he mailed the day of Ruggero's shooting to the (Minneapolis) Star Tribune and a former University of Minnesota official.

``Mario Ruggero was determined, as he put it, that I would `never work again','' read one memo in the packet. Costalupes wrote that he had been struggling to survive without an income for six years.

On the day of his suicide, Costalupes took a loaded revolver to the office of Shelly Chou, dean of Minnesota's medical school. When told Chou was busy, Costalupes tried to interrupt him, but mistakenly yanked open the door of a broom closet.

After a struggle with a security officer, Costalupes drew his weapon and killed himself.