A federal grand jury in the District is investigating an unidentified man for using Twitter to allegedly threaten former presidential candidate and member of Congress Michele Bachmann, according to a court opinion made public Thursday.

U.S. District Judge Royce C. Lamberth disclosed the investigation in a 13-page ruling that denied the user’s request to quash a grand jury subpoena seeking his identity from the social-networking site. Lamberth said the investigation arose from the man’s “professed desire to engage in sadomasochistic activities with” Bachmann (R-MN).

The tweets are too offensive to print, and Lamberth called them “extremely crude and in almost incomprehensible poor taste.”

After learning about a particularly vulgar tweet that involved Bachmann in August, a grand jury subpoenaed Twitter for the man’s identity. Twitter alerted the user — identified by Lamberth only as Mr. X — to the subpoena, and he filed a motion in the District’s federal court to quash it.

Law enforcement agencies routinely subpoena information from Twitter and other social-networking sites to gleam information about potential criminal activity. In this case, Lamberth wrote that the government has a compelling interest in investigating the threats against Bachmann and needs the man’s identity to properly assess them.

However, Lamberth added that he doubted the man would ever be indicted because there needs to be a “true threat” against Bachmann for a crime to have been committed.

“There appears to be nothing serious whatsoever about Mr. X’s Twitter page,” the judge noted, “except perhaps the severity of mental depravity that would lead a person to produce such posts.”