How serviceable is the word "victim," that it can be applied equally to a 17-year-old Vietnamese American schoolgirl who, one warm April day in 1977, was attacked in the apartment complex where she lived with her family in Queens, New York, carried to an empty apartment, raped, sodomized and strangled, and to her murderer, a 30-year-old, unemployed ex-Marine and neighbor of the girl. These are the uses David Haward Bain makes of the word in his study of the crime, "Aftershocks: A Tale of Two Victims."

It is an unfortunate title, because it puts in the reader's mind, when he knows the story in its simplest terms, the suspicion that Bain is morally callous, that he is so anxious to understand the criminal he neglects the true victim. This suspicion lingers, but I also feel an unexpected sympathy for Louis Kahan, at whose hands -- whose literal, bare hands -- Le My Hanh so horribly died.

Bain's thesis, that Kahan is a lifelong victim, both of an uncaring family and of our society at large, is familiar enough; in fact, it amounts to a first law of criminal psychology. But there is a twist to this story: Kahan is more specifically a victim of his Marine Corps training, which began when he enlisted at the age of 17, and of his combat experience in Vietnam, where, according to Kahan, he observed or participated in the rape and murder of many Vietnamese women suspected of being Vietcong. He also lived in constant fear for his own life and watched many of his comrades maimed or killed on senseless patrols or search-and-destroy missions. Bain, who is described as having been "active in the antiwar and antidraft movements," sets out to prove that when Kahan killed My Hahn, nearly a decade after his experience in Vietnam, part of him believed he was back in that country interrogating a suspect.

Several chapters of the book are filled with tales of atrocities Kahan says he witnessed, participated in or heard about during his 10 months in Vietnam. Beheadings, mutilations of the dead, the murder and rape of civilians, including children -- all these are made to seem common practices of Marines in Vietnam. In the first atrocity Kahan saw, a Marine offered a chocolate bar to a Vietnamese child, and while the child ate it the Marine dripped liquid fuel from a flamethrower on him, and ignited it.

Bain writes this about rape during field interrogations:

"The procedure in the units to which Kahan was attached was to isolate a woman from the rest of her family and village. She would be tied up, threatened, and raped regardless of what she told her captors. . . The men took turns as each occasion arose, thus reinforcing the credo that 'they were all in it together'; they had all participated. There were no exceptions, and there were no objections."

Is all this true? What is Bain's source for his information? Apparently he relies largely on what Kahan told him, although he says other Vietnam veterans have told similar stories. But were such atrocities routine? If not, then Bain does an unforgivable disservice to the Vietnam veteran who did not commit such crimes.

When Kahan returned from Vietnam in early 1967, he faced the same difficulties as so many other returning veterans: a reluctance among employers to offer them jobs; hostility from Americans who disapproved of the war, especially on college campuses; an incompetent Veteran's Administration. And he had other problems of his own: a "fiance" who had become pregnant and had married another man; a hostile father; an indifferent mother.

By the time he murdered My Hanh, Kahan had lost the ability to function: he had been living for two years in his mother's apartment (his father had died) without a job, rarely leaving the house, becoming increasingly delusional. A general feeling that he was in danger became particularized when Vietnamese refugees began moving into his neighborhood; he believed them to be the enemy.

There was no doubt in the minds of the psychiatrists who examined him in the months after his crime that Louis Kahan should not be held legally responsible for My Hanh's murder. At the trial, the doctor testifying for the prosecution oddly made a far stronger case for Kahan's insanity than the doctor for the defense.

The judge in this book is cranky and impatient; he seems determined to over-simplify Kahan's story, to dismiss with suspicion the reports of the psychiatrists. If these characters had metaphorical roles, the judge would represent the society that has treated Vietnam veterans with such indifference. Of course the judge in fact represents society, and never more so than when he angrily admits that Kahan is not legally guilty of his crime, but adds, "He broke a little twig; a little girl." "I didn't want to do it," the judge says of his decision, "I had to do it."

To research "Aftershocks" Bain talked to Kahan, My Hanh's father and the attorneys on both sides, and he consulted and quotes at length from the trial record; he came away with a bookful of information. Details are what create sympathy in a reader for a character, and the more we know about Louis Kahan and My Hanh and her family, the more we care about them. But the history of this case could have mattered so much more if Bain had been able to get imaginative purchase of his material. Nonfiction writing at its best is as much a work of the imagination as fiction writing is; some of our most powerful writers -- among them, Capote, Mailer and Didion -- have proved this by creating important works out of the formless facts of other murders.