Update 11/21/12: On November 19, Facebook received a letter and affidavit purporting to be from federal prisoner James Charles Kopp, of the U.S. Penitentiary in Canaan, Pennsylvania, alleging that the earlier “motion to intervene” filed on Kopp’s behalf was filed by an imposter. Facebook then filed the new letter and affidavit with the court. They are here.”

Someone claiming to be the incarcerated murderer James Charles Kopp, has written a letter to the federal court in Buffalo claiming ties to Paul Ceglia, the man who is suing for 50% ownership of Facebook. Ceglia was himself arrested and criminally charged on October 26, with having fraudulently manufactured his federal court claim against Facebook.

The letter, drafted as a “motion to intervene” in Ceglia’s federal civil suit against Facebook (FB) and CEO Mark Zuckerberg, purports to have been written on November 2 by Kopp, who was convicted in 2003 of murdering abortion doctor Barnett Slepian in 1998. A U.S. Magistrate Judge ordered the letter filed in the public court docket yesterday.

According to the Buffalo News, which appears to have first reported on the letter, the letter was mailed from the Canaan Federal Penitentiary in Pennsylvania, the institution where Kopp is, in fact, serving a life term, but prison officials “said they could not confirm the authenticity of the letter.”

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Among many wild claims in the letter, the person purporting to be Kopp claims that Ceglia and he have been friends since 2008, and that Ceglia admitted to him in letters that “he was going to lie and create a fraud lawsuit” to get money to hire Kopp a top-notch attorney, ideally Bruce Cutler, to help get him out of prison. The person also claims to now “support all abortions” and says “I denounce the lambs of Christ” and “I’m a changed man.”

Ceglia is in custody, unavailable to comment. Asked by Fortune to comment on the letter, Ceglia’s attorney, Paul Argentieri of Hornell, N.Y., responded in an email, “The court has created a scheduling order about Kopp’s letter. Thus, you’ll have to be patient until Mr. Ceglia files his declaration.” Asked if the letter was really written by Kopp, he responded, “Honestly, I have no idea. The whole thing appears to be phantasmagorical to me.” U.S. Magistrate Judge Leslie G. Foschio, of the Western District of New York, has ordered responses to the letter to be filed by November 19.”

A spokesperson for Facebook also declined comment on the letter.

Ceglia sued Facebook and Zuckerberg in June 2010, claiming that Zuckerberg had promised him a 50% share of the project that became Facebook in a contract signed in April 2003. Facebook and Zuckerberg have contended that Ceglia’s claims are fraudulent and that the contract he appended to his complaint was forged. Last week, federal authorities charged Ceglia with mail and wire fraud in Manhattan, evidently endorsing Facebook and Zuckerberg’s account of events.

Here is the letter: Kopp Letter