A California State University at Los Angeles professor was stabbed to death and beheaded early Monday in what police investigators believe to be a murder-suicide that was perpetrated by a former student she had once supervised.

Police officers found the decapitated body of Glenda Vittimberga, 37, a professor of education, in her home in Pasadena, Calif., after receiving a telephone call from the suspect's sister. While investigating Ms. Vittimberga's death, the police received word that the suspect, Mark Stephen Guerrero, had died in a traffic accident.

Mr. Guerrero, 38, committed suicide by stripping naked and jumping in front of an 18-wheel truck on Interstate 15, about 36 miles east of Pasadena. Janet Pope, a spokeswoman for the Pasadena Police Department, said officials were testing items and substances found in Mr. Guerrero's car, including blood, to see if they could be tied to Ms. Vittimberga.

Mr. Guerrero "is the primary focus of our investigation," said Ms. Pope. However, she said that until the forensic evidence returns from the laboratory, investigators are not ruling out any possibility.

The exact nature of the relationship between Ms. Vittimberga and Mr. Guerrero remains unclear. Mr. Guerrero worked at the university's diagnostic-testing center until 2002 under Ms. Vittimberga's supervision.

Ms. Pope said the police believe that the pair were romantically involved at some point and that the murder had resulted from a domestic dispute. But officials at the university said they have no knowledge of a relationship, and local newspapers have reported that friends of Ms. Vittimberga have denied the existence of a relationship.

Mr. Guerrero received a master's degree in education from the university in 2000 and continued to take classes in psychology until 2002. At the time of his death, he was not enrolled or employed by the university.

In a prepared statement, university officials called Ms. Vittimberga a "rising star" and "a woman who dedicated her life to the education of others."