On occasion (all the time in Prince William County, VA), when a non-citizen is pulled over or arrested by law enforcment for traffic or criminal violations, ICE place a detainer, a hold, on that person. A detainer is a request by ICE for the local police department or jail to hold the person for up to 48 hours while ICE determines if they should take that person into immigration custody.
While ICE is getting better, the 48 hour rule is not complied with as much as should be the case. ICE issues its detainer request on form I-247 which is shown below. As you can see, in CAPS and bolded is the language "MAINTAIN CUSTODY OF ALIEN FOR A PERIOD NOT TO EXCEED 48 HOURS."
Ricky Malik, Esq.