According to news outlets reporting:
He is a former grad student who graduated last year with a doctorate in Financial Engineering
He is a greencard holder and is married to a citizen of the US...who is 8 months pregnant. Together they lived in University housing off campus which is where he was arrested.
He is an Algerian citizen of Palestinian descent who was raised in Syria
He worked in London before coming to the US for grad school at Columbia
The Trump administration says that it will rescind his green card and deport him for "working with Hamas" to spread antisetic and pro-Hamas views...which is a designated terrorist originazation. It is still unknown if he will face charges in the US or just be deported.
He was one of the main organizers of the protests last year on Columbia's campus was active in the CUAD (Columbia University Apartheid Divest) and served as a primary negotiator between the protesters and the University Administration during the encampment last spring.
He was one of the few protesters that didn't wear a mask to hide his identity.
No one knows where he was taken to. It was originally thought to be at a processing facility in NJ but rumors now say he was taken to Louisiana.