The Federal Bureau of Investigation says that more than a month before Dr. George Tiller was shot and killed, it received an anonymous letter warning about the man now charged in the case.

FBI spokeswoman Bridget Patton says the April letter warned that Scott Roeder would physically harm Tiller or any other abortion provider.

The letter turned out to have been written by Mark Archer. He and his wife are in the midst of a bitter custody battle with Roeder over a child Roeder fathered.

Roeder has been charged with first-degree murder and aggravated assault in Tiller's May 31 killing.

Patton says the agency found no specific, credible threat in the letter.