Police investigating the fatal shooting of three professors by a student at San Diego State University say the 36-year-old suspect's thesis had been failed once already. A repeat would probably have meant the end of his university career.

Frederick Davidson, an army veteran, produced a 9mm handgun at the meeting where he was due to defend his master's thesis in engineering. He fired 20 shots, killing the three men on a review panel.

The first to die was his adviser, Chen Liang, an assistant professor of mechanical engineering and described as a rising star in his field. Associate professors Constantinos Lyrintzis and D. Preston Lowrey were shot as they tried to flee.

Mr Davidson, a San Diego student since 1987, was co-author of some of the 70 articles and papers Mr Liang had published. But associates said his feelings towards his adviser swung between admiration and resentment for a man he began to accuse of exploitation.

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Mr Davidson was a loner who reportedly struggled to get a job after earning a bachelor's degree in aerospace engineering in 1991. He returned to the university where he found part-time jobs while he worked on his thesis on shape memory alloys - metals that return to their shape when twisted or bent.

Three students in the room to observe his defence were unharmed.

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Campus staff said there were no plans for metal detectors or other security measures. But they said the incident underlined the need to reach out to university members showing signs of stress.

Doug Tuttle, a past president of the International Association of Campus Law Enforcement Administrators and a security officer at the University of Delaware, said: "It seems to be a trend that people find themselves unable to cope."