That has already happened. Why are you mad about that?
He'll get a butt load of due process, now. He can call witness - including Senator Van Hollen. He can compel Van Hollen, or whoever else he wants to call to appear in court, go under oath, and answer all questions. There is no Senatorial Privilege. He can have his wife testify as a character witness, but I'm not sure if he can compel her to cover any black eyes with makeup. Not legally.
The prosecution can compel Van Hollen to appear also, if Abrego Garcia does not. But, as we know, if Van Hollen is innocent, he has nothing to worry about.
I'm sure his boss keeps careful record of who he sent Abrego Garcia to traffic give a ride to work. So he can subpoena his old boss to hand over those records so he can call those riders as witnesses.
Of course the prosecution can also subpoena that guy and find those hard working employees. They can call in experts on tattoos to clear up the mystery of Abrego's tattoos. Do they say "MS13" or "Strong Deeds Gentle Words - Maryland loves fathers!"
Are you not looking forward to all that process that Abrego Garcia is due?