Many jails routinely screen individuals for immigration status and notify ICE of any non-citizens. ICE then investigates the individual and, if they believe there are grounds for removal (aka deportation), then they issue a charging document (Notice to Appear or "NTA") and, in many cases, they assume physical custody. Whether a DWI/DUI is a removable offense varies based on the language in the state law. In some states, a DWI/DUI may be considered a crime involving moral turpitude (CIMT), which renders a permanent resident removable if the conviction occurs within five years of the grant of permanent residence. Alternately, if he has prior CIMT convictions, he can be deported for 2+ CIMTs at any time. If the DWI/DUI involved drugs and not just alcohol, he could be deported for a drug offense. Or, as so often happens, ICE may issue the NTA when he really isn't removable, he may sit in custody waiting for a hearing before an immigration judge (often by videoconference), and if he is fortunate enough to have the money to hire an attorney or to find pro bono assistance, the judge may agree the DWI/DUI is not a deportable offense and terminate the proceedings. At that point, however, he may have spent weeks or even months in detention.