Almost two weeks after a Bethesda man, his wife and their infant daughter were found knifed to death, Detroit police are still searching for a suspect.

David Saul Berkley, 26, a graduate of Walt Whitman High School who was studying for a doctorate in anatomy at Wayne State University, was attacked on the street in a residential neighborhood near the campus.

Police speculate that the killer then used Berkley's keys to enter his apartment, where Berkley's wife, Aline, 25, a law student at the University of Detroit, and their nine-month-old daughter, Jessica, were stabbed fatally.

The Berkleys had planned to spend Christmas and New Year's in the Washington area with his parents, then travel today to California to be with Aline's parents, Norman and Aline Felton.

The murders of Aline Berkley and her daughter were not discovered until Aline's father, after failing to hear from her, telephoned the building manager of the Berkley's apartment on Dec. 21 and persuaded him to enter the apartment.

With the discovery of the bodies there, police were able to identify a body, classified only as "unknown man 192," as David Berkley. His body had been found lying in the 3 foot-wide walkway between two buildings two days before.

Berkley was last seen alive by a fellow student at 5 p.m. on Dec. 18 at the lab where Berkley was conducting research on problems of the cornea under a grant from the National Eye Institute in Bethesda.

His sister, Florence Berkley of Bethesda, said Berkley had called home that same night and made plans for the Christmas holidays. He was happy because he and his wife had finished one more term (the university would later report he had made all 'A's in his last semester), and because he was coming home soon. As he and his sister talked, Jessica gurgled and laughed in the background while her mother gave her a bath.

Police speculate that sometime after 8 p.m., as Berkley was either walking home from the lab or to the lab for some late-evening catch-up work, he was assaulted. They believe the attacker forced him to an area near an abandoned building, killed him, and took his keys and identification that showed his address. The killer apparently then used the keys to enter the Berkley residence and attack two more victims.

Detroit detectives have questioned three suspects who were released after taking polygraph tests. Investigators say they are stumped for a motive.

Detroit police, in cooperation with the Detroit News "Secret Witness Program," are offering a $5,000 reward for information leading to the arrest of the killer.

A member of Berkley's family said his research would be continued by the university.