The Supreme Court reversed a prior 9th Circuit Court ruling restricting when illegal aliens could be detained and deported.
The SCOTUS ruling (full pdf below) was in favor the Trump administration, allowing federal officials to detain and deport illegal aliens after they have served their time in the U.S. for other crimes regardless of whether they were picked up immediately or later, after criminal release.
The 9th Circuit Court previously stated ICE would have to detain illegal aliens immediately after release or they would be exempt from later detainment.  SCOTUS eliminated that restriction and affirmed detainment and deportation at any time after criminal release.  The ruling was 5-4 with Justice Alito announcing the majority judgement of the court below:

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