In her compelling book Halfway Heaven (219 pages. Doubleday. $23.95), Melanie Thernstrom offers an eloquent explanation of how these two lives intersected so tragically. A Harvard graduate whose father teaches history at the university, Thernstrom is an insider who draws a disturbing portrait of an institution poorly equipped to handle the emotional problems of students from different cultures. Tadesse sought help from Harvard’s counseling center. Yet no one apparently understood her emotional fragility. Thernstrom suggests that may be in part the result of Tadesse’s cultural background; she found it extremely difficult to talk about what she called her ““social problems.’’ Instead, she wrote her thoughts in journals Thernstrom quotes from (they are part of the public record). Her conclusion: Tadesse was ““an intelligent, insightful, strong-willed person using all those capacities to fight as hard as she could for mental health–and losing, day by day, hour by hour.''

In this deteriorating state, Tadesse saw Ho, a friendly and popular student, as her last chance to make a human connection. When Ho chose to room with someone else the next year, Tadesse struck. Could the tragedy have been averted? Although Thernstrom clearly believes Harvard could have done more, she also points out how difficult it is to spot a student in trouble. Thernstrom herself could have helped. She met Tadesse briefly when teaching creative writing at Harvard; Tadesse applied for the course, and Thernstrom rejected her. Later Tadesse asked her to reconsider, and Thernstrom didn’t–because, she says, Tadesse’s writing sample ““made no impression.''

Harvard has been highly critical of ““Halfway Heaven.’’ University officials contend that Thernstrom exploited her insider status to gain access to confidential material. But Thernstrom says the ““confidential’’ material was a university phone book and her interviewees always understood she was talking to them in her role as a journalist.

In fact, her book works not just as an account of a murder but as a study of how a reporter explores such a crime. Her reluctance to confront Tadesse’s family after traveling all the way to Ethiopia conveys the emotional ambivalence experienced by most reporters in such circumstances. What instinct will win out? Curiosity or timidity? Fortunately, Thernstrom was ultimately tough enough to ask all the right questions.