It should come as no surprise that Dr. John Kappler finally took someone's life.

For over a decade, Kappler, an anesthesiologist, said voices instructed him to hurt other people. In 1975, he drove his car into another automobile on a California freeway. When the other driver got out of the car, he took it and was involved in another accident. In 1980, the voices told him to administer the wrong drug during surgery to a patient who suffered a cardiac arrest. The patient recovered and no charges were filed. In 1985, he was charged with attempted murder for allegedly turning off the the life support system to another patient; charges were dropped due to insufficient evidence, and Kappler retired from his practice shortly thereafter.

Last spring, Kappler was visiting Massachusetts from his home in California. On the afternoon of April 14, he later told police, the voices told him to drive his car onto a jogging path in Cambridge, killing my close friend and colleague Paul Mendelsohn. Kappler then accelerated and struck a 32-year-old single mother who was returning home from shopping. She survived with a broken pelvis and leg, as well as serious injuries to her face, head and neck. Kappler had apparently never met either victim and he ran from the scene.

At his murder trial, his lawyer introduced evidence that Kappler had been diagnosed, at various times since the 1960s, as suffering from schizophrenia, manic depressive illness or atypical psychosis.

What Kappler took away is incalculable. Paul Mendelsohn would have been a chief resident in psychiatry at New England Medical Center in Boston this year. His gentle manner and tireless ear had helped him mature into someone colleagues already called a "doctor's doctor."

We had worked alongside one another through the grueling pressure of our internship year, becoming the kind of friends who hold pieces of each other within. Not long before he died, we had dinner. Paul was looking forward to returning home to California with his wife for the final six months of his training. We marveled at how quickly time was passing and agreed to spend more of it together.

But late on the night of April 14, an anesthesiology resident from Massachusetts General Hospital called me at home. The two of us had graduated from medical school together.

"We have a doctor in the intensive care unit, unconscious, who was jogging and got hit by a car," he said. "He was wearing a beeper from your psychiatry department. Who would have been carrying that today?"

"I don't know. What does he look like?" I asked.

"Well, that's just it. Between the accident and the work we did, there's too much swelling. Someone said he might be from California."

"My friend Paul Mendelsohn is from California," I replied. Even having spoken it, the link seemed unreal. Despite all the young people I have watched die painfully on medical wards, I irrationally reassured myself that Paul's death was unlikely because he was too good to die.

"We've heard it might be him," he started. "Listen, why don't I meet you in the hospital lobby? There are some other residents from your program here."

I hesitated. "Look, anyone from the program would know if it was Paul. He's tall with red hair," I argued.

"Keith, I don't think your friend's going to make it."

Paul was not technically dead when I arrived at the ICU. I could not recognize him. The leap -- from a strong and healthy man of 32 to the disfigurement I saw before me -- was incomprehensible. His life and his death seemed disconnected. Against nearly irrefutable evidence to the contrary, I fantasized a case of mistaken identity. My strongest image of that night is of walking his widow to his bedside and watching her draw back the bedsheet and identify him by the contour of his chest. I hadn't thought a woman could know a man by his chest.

The beeper became an instant symbol of death to me because it had helped the doctors identify Paul. I actually balked at accepting one from a colleague the next time I was on duty overnight..

I stayed at the ICU until early morning, not wanting to leave, as if my lingering could stop time. Kappler, meanwhile, had fled the scene of the accident on foot. He traveled to New York City and checked into a psychiatric hospital. He was returned to Massachusetts several days later to face trial for second-degree murder, assault and battery with a deadly weapon, driving to endanger and two counts of leaving the scene of an accident.

He pled not guilty. The voices, Kappler said, had plagued him again, this time insisting he drive up over the curb and onto the footpath to run down his victims.

I believe I wanted Kappler to be insane. At least, that would allow me some understanding of the forces resulting in Paul's death. I would feel justified in allowing compassion for a sick person to mingle with my uncomfortable rage at his actions. I could let intellect buffer emotion.

At the same time, my mind took the liberty of painting Kappler as enormous and powerful, with danger in his eyes. It satisfied some illogical equilibrium in me that my friend's killer should be physically imposing enough to claim his life.

But when I attended his murder trial in Cambridge last December, I was disappointed to discover that the real Kappler was small and thin. His eyes were empty, and he seemed weak.

His trial lasted more than two weeks. After deliberating less than three hours, the jury found him guilty of all charges and sentenced him to life imprisonment. The verdict didn't hinge on the issue of whether Kappler was mentally ill. But it did turn on the question of whether he was legally insane at the moment that he drove his car onto the jogging path. Jurors decided he wasn't, possibly persuaded by the prosecution's argument that he had resisted previous commands by the voices, such as one that ordered him to commit suicide.

The verdict, predicated on Kappler's ability to choose right from wrong, leaves my intellect in uncharted territory. If I cannot explain his behavior as insanity, I am forced to contemplate what would lead someone to kill a person he has never met.

Everyone who has shared this tragedy with me has struggled with the same question. They still wonder what relationship John Kappler and Paul Mendelsohn might have had before the murder.

The desire for a connection is a plea for order in this fatal chaos, a bit of firm ground from which to view Kappler's motivation. If he wasn't crazy, I suppose we feel he should have been angry.

If John Kappler was neither, I am forced to confront the possibility of human evil, the idea that people might do terrible things to one another because they want to. Incarceration is one way our society tries to correct or contain that impulse. But like Gandhi, who conceived of all crime as illness, some would say that the only true cure is for the victims to love the perpetrators, to meet their evil with open arms and thereby render it impotent.

No one can say for sure what force took Paul Mendelsohn from this world. Nothing will bring him back. But if anyone was on his way to being able to absorb evil and survive with his soul intact, it was Paul. Keith Russell Ablow is a writer and senior resident in psychiatry at New England Medical Center in Boston.