The FBI obtained a search warrant to access former Milwaukee County Sheriff David Clarke’s personal email in March, according to a federal court filing made public this week.

An affidavit dated March 7 explained the FBI wanted access to Clarke’s personal Gmail account for an investigation into an incident between Clarke and fellow airline passenger, Dan Black, in January.

Black sued, claiming he was unlawfully detained by six uniformed deputies and two K-9 dogs after a squabble with Clarke aboard an American Airlines flight in January.

Special Agent Jennifer Walkowski requested the search warrant for the FBI after being pointed towards the emails by Milwaukee County auditors.

Walkowski presented the court with a photocopy of an email from Clarke – at the address dclarke.cowboy@gmail.com – referencing Black’s formal complaint which read: “Sheriff has taken this asshole’s compliant under advisement and summarily determined that he can go to hell. The next time he or anyone else pulls this stunt they may get knocked out. Sheriff does not have to wait for some goof to assault him.”

Another piece of evidence presented in the request was a post on the official Milwaukee County Sheriff’s Office Facebook page which displayed a picture of Black with the caption: “CHEER UP SNOWFLAKE… IF SHERIFF CLARKE WERE TO REALLY HARASS YOU, YOU WOULDN’T BE AROUND TO WHINE ABOUT IT.”

According to a letter from the U.S. Attorney’s Office, the criminal civil rights case was officially closed in May due to a lack of evidence to prove a violation of a federal statute beyond a reasonable doubt. However, his civil rights lawsuit is still pending in federal court according to the Milwaukee Journal Sentinel.

Walkowski has requested that the warrant application be sealed so that people possibly being looked at in the probe would not be made aware of the FBI's involvement in the probe.

Clarke, who resigned from his role as sheriff in August and is a longtime Trump surrogate, wrote a brief email to Law & Crime saying that the FBI investigation closed in May.

“You’ll have to ask FBI why the return of the search warrant took so long,” Clarke said. “I was notified by Google that the search warrant request was made in March.”

Clarke issued a pointed tweet Saturday complaining of "FAKE NEWS" reports of an FBI investigation.