State police have arrested the prime suspect in a case of assault, larceny and malicious destruction of property at Widener Library, officials of the Harvard University Police Department said yesterday.

Andrew A. Willis, a resident of South Easton, was stopped for illegally walking along the Southeast Expressway on Friday afternoon.

State police officials turned Willis over to the University police after they were able to link him with the crimes committed at the library last week.

Last Tuesday, Willis allegedly threatened a library attendant, smashed a display case and stole a 200-year-old ceremonial gold-plated key from the library's Widener Room.

The room houses a rare edition of the Gutenberg Bible, as well as the personal book collection of Harry Elkins Widener '14, for whom the library is named.

The crystal inkwell that Wills used to threaten the library attendant was also recovered on Friday.

Willis is being held at the Middlesex County Jail and will be arraigned this morning.