If you know the detainee's full name, date of birth and country of birth, you may be able to use the ICE detainee locator system. Keep in mind that their system isn't always up to date and if the detainee provided an assumed name or if they were already returned to their home country, they may not appear.
The direct link to the detainee locator page is
Matthew C. Thomas, Esq.
Thomas & Jefferies, PLLC
1990 W. Camelback, Suite 307
Phoenix, AZ 85015