An anti-evolutionary Christian extremist suspected of sending threatening letters to biology professors at the University of Colorado has gone on the lam, according to a staff member familiar with a police investigation into the matter.

Police at the University of Colorado say they know the identity of the individual who sent threatening letters to several biology professors who taught evolution. However, the police won't name the individual until they make an arrest, said detective lieutenant commander John Kish.

Staff at the biology department have been issued a picture of Michael Korn, a messianic Jew, who has said he is the "messenger of God" and runs a website called JesusOverIsrael.

"(Korn's) picture has been circulated on flyers saying: 'If you see this guy dial this number,'" said Jeffry Mitton, professor and chair of the department of ecology and evolutionary biology, and one of the instructors who received the threats.

"He does not seem to be around," Mitton added. "We believe he is gone, we know not where."

Korn was seen distributing flyers suggesting the instructors were "child molesters" for teaching evolution to students.

In the last year, a series of threatening letters and e-mails – the most recent referring to "killing the enemies of Christian society" – were sent to several professors at the biology department in Boulder. (Read more on the developing story in the Wired Science blog.)

How serious are the threats? It's unknown, but the letters appear to mark one of the most aggressive statements yet in a growing debate over the place of evolutionary theory in education.

At a time when the Virginia Tech and Columbine school shootings are fresh in Americans' minds, the threats are particularly worrisome for Mitton and his colleagues.

"Debate is fine," said Branson Hilliard, a spokesman for the university. "But threats and invocations of violence and intimations of violence are not what go on at a college campus. Students cannot learn in a context of fear."

At first, professors considered the letters a nuisance, but the most recent threats were delivered after business hours when the biology building was closed, and police were called. The letters were slipped under professors' doors in envelopes sealed with tape and decorated with skull and crossbones.

This week, biology professors met several times with police about increasing security and canceled extracurricular activities in their building.

"There have been a lot of meetings about what times the doors will be closed…. We've increased not only patrols around the building but also (have police doing) walkthroughs," said Mitton.

According to Mitton, Korn appears to have skipped town. Police visited Korn's apartment, but found that he and his wife were gone. The apartment had been sublet and his wife had quit her job, said Mitton, who added he has met and spoken to Korn on several occasions.

Contacted earlier this week, Korn declined to address specific questions from Wired News, but he forwarded e-mail messages he had previously sent to the Denver Post, which published a story on July 10 about the case.

His e-mail message didn't admit to sending the recent threatening letters, but tried to explain their meaning.

"The skull and crossbones on the envelopes given to the EBIO (evolutionary biology) professors symbolize the human fossils about whose age they constantly lie to the public," Korn wrote.