Sitting on the tarmac at the Dallas/Fort Worth International Airport on Jan. 15, Milwaukee County Sheriff David A. Clarke Jr. sent a text message to one of his captains after a brief verbal exchange with a passenger.

The sheriff explained in the text what should be done when Riverwest resident Dan Black got off the plane.

"Just a field interview, no arrest unless he become an asshole with your guys," Clarke wrote Captain Mark Witek. "Question for him is why he said anything to me. Why didn't he just keep his mouth shut?"

"Follow him to baggage and out the door," Clarke continued. "You can escort me to carousel after I point him out."

A copy of the text messages was provided by an attorney for Black, who is suing the sheriff, Milwaukee County and several unnamed deputies over the incident.

OPINION:The hits keep coming for Milwaukee County Sheriff David A. Clarke Jr.

Records show the matter, which has drawn national attention, was big enough that federal investigators looked at Clarke and his staff's handling of the case. Clarke has said he is taking a job as assistant secretary at the U.S. Department of Homeland Security, though officials have not confirmed this.

Assistant U.S. Attorney Mel Johnsonsent a letter on May 3 saying his office had decided not to file charges for civil rights offenses.

"Our decision is not meant to affirm the wisdom or propriety of what occurred," Johnson wrote to William Sulton, attorney for Black. "It reflects only our belief that it would be difficult or impossible to prove a violation of the only federal statute available to us …beyond a reasonable doubt."

Sulton declined to comment on the letter and text messages.

Fran McLaughlin, spokeswoman for Clarke, said regarding the federal probe: "The sheriff said he doesn’t know what you’re talking about." She did not address the text messages and other documents.

Black, 24, says he was detained, interviewed and escorted out of Mitchell International Airport on Jan. 15 by a half-dozen deputies after a brief run-in with the sheriff on the plane. He says in the federal suit that he was the victim of an unlawful stop and arrest.

Since Black went public with his complaint, Clarke has threatened and belittled his fellow passenger, calling Black a "snowflake" and saying anyone, including Black, who harasses him on an airplane might get "knocked out."

But now Clarke is giving his version of the events on the plane, which matches Black's account, except in a couple of details.

In a response to the lawsuit, the sheriff's attorneys say the run-in occurred as Clarke sat in his first-class seat on the American Airlines flight and Black boarded the plane.

"Plaintiff stopped adjacent to Sheriff Clarke's seat as Plaintiff boarded the plane and asked him if he was Sheriff Clarke," the sheriff's attorneys wrote. "Sheriff Clarke responded in the affirmative.

"Plaintiff then, while standing over Clarke and in very close proximity to Clarke given the confines of the airline cabin, and in a physically threatening manner, stared at Clarke and shook his head at him for a prolonged period of time," the lawyers wrote. "Clarke asked plaintiff if he had a problem with him, to which plaintiff did not respond."

In his suit, Black said he saw Clarke — decked out in Dallas Cowboys attire instead of his signature Stetson — and wondered if he was the sheriff. So Black said he asked Clarke, who confirmed his identity. Black said Clarke countered by asking Black if he had a problem. Black said he responded by saying he did not.

He has not said he stood in a "physically threatening manner" over the sheriff, who is a couple of inches taller than Black.

Black's version of events matches what he told Deputy Sheriffs Steven J. Paull and Jeffrey Hartung, according to their brief notes. "Suspect was FI'd (field interviewed), escorted to ticketing for ride and released without further incident," Paull wrote.

Airport audio shows that the sheriff or his staff were in contact with American Airlines officials about the incident. At 1:13 p.m. on Jan. 15, an airlines representative called Milwaukee County deputies about Clarke.

"Sheriff Clarke is coming off our 1534 flight," said the female airlines worker. "They called and said there are three passengers that are not being respectful to him."

Clarke has mentioned only his conflict with Black.

If the sheriff was intimidated or frightened by his exchange with Black on the plane, that didn't seem apparent from video of him after he exited the plane in Milwaukee.

One video shows five uniformed officers with a police dog — not six as Black had earlier alleged — waiting for Clarke and Black at Gate 54 of Concourse D at the Milwaukee airport.

Clarke is one of the first to exit the plane, saluting his staff when they greet him. Black follows 2 1/2 minutes later and two of the deputies engage him. Later video shows Clarke being escorted by a captain, a sergeant, a deputy and the dog near Gate 30. Black is accompanied by two deputies about nine minutes later.

The video was obtained by Sulton via an open records request. He received the text messages and audio from disclosures resulting from the litigation.

It is not clear how much of this information was available to federal authorities. Two assistant U.S. attorneys and an FBI agent oversaw the probe.

In his letter, Johnson wrote that the decision to drop the case was based on records and interviews. He added, "Of course, the decision could change if additional information came to light."

Milwaukee County auditors are also conducting their own investigation into whether Clarke was guilty of waste or abuse of county resources. But Clarke has refused to cooperate with the probe, calling it a "fake investigation."

The Milwaukee County Board gave auditors the authority to spend up to $35,000 to sue Clarke for blocking the investigation — a matter that is now on hold.

"As news developed about the sheriff's likely departure from county service, we put the matter on pause," county Auditor Jerry Heer said this week. "Our hope would be that if the sheriff leaves, his replacement would be more willing to give us the access we need to do our job."

Contact Daniel Bice at (414) 224-2135 or dbice@jrn.com. Follow him on Twitter @DanielBice or on Facebook at fb.me/daniel.bice.