WASHINGTON — Twenty-two people died in ICE custody last year. At least 30 have been shot by immigration agents since President Trump took office. And now, according to internal FBI guidance, the one federal agency positioned to independently examine those encounters is stepping back. FBI field offices nationwide were told in writing that the bureau will no longer take the lead on “assault on a federal officer” cases involving ICE and other Department of Homeland Security agents. Under the new guidance, that work moves instead to Homeland Security Investigations — ICE’s own investigative arm, operating inside the same department as the agents whose conduct would be under review.