Asgari, a professor at Iran's Sharif University of Technology, had been indicted in April 2016, accused by federal prosecutors of trying to steal secret research from Case Western Reserve University. The Cleveland school had been working on a project for the US Navy Office of Naval Research to create and produce anti-corrosive stainless steel.

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Asgari ultimately was acquitted in November after US District Judge James Gwin tossed the case by prosecutors.

Ken Cuccinelli, the acting deputy Homeland Security secretary, earlier told The Associated Press that the DHS had started to try to deport Asgari on December 12 after his acquittal. However, he said, Iran refused to recognise him as legitimately Iranian and provide him with a validated passport until late February.

Once Asgari received the passport, DHS made several attempts to fly him back to Iran, purchasing tickets for flights on March 10, March 18, March 23, April 1 and May 1, according to Cuccinelli. Each of those flights was cancelled due to the coronavirus pandemic, he said.

Asgari's supporters told The Guardian newspaper in April he had contracted the coronavirus while imprisoned.

Iranian officials had associated Asgari's release with US prisoners held in Iran potentially being freed, something Cuccinelli had been trying to downplay. Iranian officials in recent days had been saying they believed Asgari soon would return to Iran.

AP