Mahmoud Khalil has not been charged with any crime. From Khalil from unz.com:

Protests in Thomas Paine Park against the detention of Palestinian activist and Columbia student Mahmoud Khalil. Photo from Wikimedia Commons registered under Creative Commons Attribution 4.0
Mahmoud Khalil, a green card holder with permanent residency, has released his first public statement since his arrest on March 8. He was taken into custody by plainclothes Department of Homeland Security (DHS) officers in the lobby of his Columbia University apartment complex due to his alleged connection to Hamas. His statement, released Tuesday, was dictated by phone to family members from an ICE center in Louisiana.
Khalil, who has not yet been charged with a crime, said he is a “political prisoner” and expressed concern with the political and social climate in the United States that led to his arrest. He and his lawyers argue that his arrest and detainment violate his constitutional rights to free speech and due process.
Khalil’s wife, who was present at the time of his arrest, is eight months pregnant and unsure if he will be present for the birth of their child.
His full unedited statement reads as follows:
My name is Mahmoud Khalil and I am a political prisoner. I am writing to you from a detention facility in Louisiana where I wake to cold mornings and spend long days bearing witness to the quiet injustices underway against a great many people precluded from the protections of the law.
Who has the right to have rights? It is certainly not the humans crowded into the cells here. It isn’t the Senegalese man I met who has been deprived of his liberty for a year, his legal situation in limbo and his family an ocean away. It isn’t the 21-year-old detainee I met, who stepped foot in this country at age nine, only to be deported without so much as a hearing.
Justice escapes the contours of this nation’s immigration facilities.
On March 8, I was taken by DHS agents who refused to provide a warrant, and accosted my wife and me as we returned from dinner. By now, the footage of that night has been made public. Before I knew what was happening, agents handcuffed and forced me into an unmarked car. At that moment, my only concern was for Noor’s safety. I had no idea if she would be taken too, since the agents had threatened to arrest her for not leaving my side. DHS would not tell me anything for hours — I did not know the cause of my arrest or if I was facing immediate deportation. At 26 Federal Plaza, I slept on the cold floor. In the early morning hours, agents transported me to another facility in Elizabeth, New Jersey. There, I slept on the ground and was refused a blanket despite my request.
My arrest was a direct consequence of exercising my right to free speech as I advocated for a free Palestine and an end to the genocide in Gaza, which resumed in full force Monday night. With January’s ceasefire now broken, parents in Gaza are once again cradling too-small shrouds, and families are forced to weigh starvation and displacement against bombs. It is our moral imperative to persist in the struggle for their complete freedom.