The video "shocks the conscience," Lieutenant Weddington said. "This is taken very seriously in our department."
Before he approached the woman, one hears a voice in the video that Mr. Thomas says he would get $ 200 to beat and the money in his pocket.
The police said the victim, using the name Muhlaysia Booker, had been hospitalized after suffering a concussion and a broken wrist.
The episode started on Friday afternoon when Mrs. Booker, driving a black submarine driver, returned to a car in the parking lot, as the affidavit shows. The driver of the car said he was trying to get her S.U.V. from the street and pulled a gun at Mrs. Booker after she had tried to escape.
Mr. Thomas was part of a large crowd that had gathered in the parking lot according to the affidavit. According to the police, the video shows the shadow of Mr. Thomas donning gloves before beating Ms. Booker with his fists.
According to the police, people in the crowd shouted homophobic interrogations while beating.
On Sunday night, Mr. Thomas warned an officer at a gas station about a non-related matter. The officer later recognized Mr. Thomas from the video and led to his arrest.
Mr. Thomas admitted to the beatings, but denied saying anything "derogatory" according to the affidavit.
On Monday, Mr. Thomas was jailed for $ 75,000. It was not immediately clear if he had a lawyer.
Attacks on transgender people have increased, according to stakeholders. In the past year, at least 26 transgender people were killed in the United States, most of them black transgender women Human Rights Campaign, an advocacy group.
In 2017, this number was 29, the highest ever reported figure, the group said.
Mayor Mike Rawlings from Dallas said after the attack in a statement that he was "extremely angry at the violence of the mob against this woman".
"Those who did this do not show how the Dallasites talk about our thriving L.G.B.T.Q. Community, "he said. "We will not stand for such behavior.