The letters demanded the coach pay $20,000 to $30,000 or his life would be made "a living hell by doing something to (his) family," according to court documents filed Thursday.
Investigators interviewed the women named in the letters, who said they knew nothing about them and never met Coughlin. The women also identified the handwriting as belonging to Simpson, a former co-worker who they said had written threatening letters to others in the past, authorities said.
In an affidavit, FBI special agent Todd A. Berry said Simpson admitted writing the letters to get revenge against the women over what was referred to as "a work-related issue."
Simpson told investigators that he researched personal information about Coughlin's family to include in the letters, but he never thought the coach would get them and he never intended to harm his family.
Simpson is charged with mailing threatening communications, which carries a sentence of up to two years in prison and a $250,000 fine.
"We take seriously any threats to extort money from anyone," said Laurie Magid, acting U.S. attorney.
There was no Philadelphia telephone listing for Herbert Simpson and he could not be reached for comment. It was not known if he had a lawyer.
