DES MOINES, JAN. 31 -- A defendant described by prosecutors as an odd man who "wears his underwear a long time" was found guilty today of the theft of millions of dollars worth of rare books from libraries and museums.

Stephen Blumberg, 42, had pleaded not guilty by reason of insanity to four felony charges, including one of possessing 21,000 books stolen from libraries and museums in 45 states and Canada. The other counts related to thefts of musical instruments and stained glass windows.

Blumberg, who had been free on bond, was immediately taken into custody after the federal court jury deliberated four hours and returned the guilty verdicts. His sentencing was set for April 26.

Earlier in the day, summing up 6 1/2 days of testimony, a defense attorney pursuing the insanity defense said Blumberg lives in a "time warp" and was driven by delusions to steal rare books from all over the country. Defense psychiatrists said Blumberg had schizoid tendencies and a family history of mental illnesses.

But prosecutor Linda Reade sided with a government psychiatrist who said Blumberg was simply angry, not insane. "This man stole the cultural history of the United States, but he is nothing more than a thief."

Much was made during the trial of Blumberg's unkempt appearance. He wore the same sweater and pants throughout, changing shirts once. "Mr. Blumberg doesn't like to take baths and he wears his underwear a long time, but that doesn't make him mentally disturbed," Reade said.