Allegations of inappropriate behavior by Garrison Keillor were more substantial than indicated in November when Minnesota Public Radio severed ties with him, according to a letter the network sent its members on Tuesday.

The letter from the network’s president, Jon McTaggart, said that MPR received a 12-page correspondence on Oct. 22 from the lawyer for a woman who had worked with Mr. Keillor on “A Prairie Home Companion” that described “dozens of sexually inappropriate incidents directed at her client over a period of years.”

The woman’s lawyer detailed “many of the alleged incidents, including excerpts from emails and written messages, requests for sexual contact and explicit descriptions of sexual communications and touching,” according to Mr. McTaggart. The woman has not publicly identified herself.

It was her allegations that prompted the network to open an independent investigation. “We told Garrison that we were doing so,” Mr. McTaggart said.