CHICAGO (Reuters) – A Northwestern University professor who is a primary suspect in a fatal stabbing in Chicago last week was spotted a day after the killing in Wisconsin, where he made a $1,000 donation to a library in his alleged victim’s name, police said on Friday.

Police have been searching for Wyndham Lathem, a 42-year-old associate professor of microbiology and immunology at Northwestern, and Andrew Warren, 56, who works at Britain’s Oxford University, since discovering the body of a slain 30-year-old man in Chicago on July 27.

Police have not identified the victim or said what if any relationship he had with Lathem and Warren.

The day after the body’s discovery, a man handed $1,000 in cash to a librarian at the public library in Lake Geneva, Wisconsin, a resort town located about 80 miles (130 km) northwest of Chicago, according to Ed Gritzner, a detective lieutenant with the Lake Geneva police department.

The man who made the donation was Lathem, Chicago police spokesman Anthony Guglielmi said.

The man declined to identify himself at the library and requested that the donation be made in the victim’s name, Gritzner said.

Gritzner said he did not know, and Guglielmi declined to comment on, what led Chicago police to Lake Geneva.

Police have restricted Lathem’s passport and Warren’s visa, and arrest warrants have been issued for both men.

Northwestern said that Lathem, a faculty member since 2007, had been placed on administrative leave and banned from the Chicago-area school.

Warren is a senior treasury assistant at Somerville College, part of the Oxford University network, the college said.