Grennell, 26, of Marcellus, New York, was serving in the nation’s capital to help with security efforts after a riot occurred at the U.S. Capitol on Jan. 6 that left five people dead.
Grennell was found unresponsive while off-duty in his hotel room, according to 9WSYR, a local Syracuse news station. He was found by his roommate, who called 911 and gave him CPR while waiting for emergency personnel to arrive.
Grennell was pronounced dead on Thursday, and his death is being investigated by local police.
Around 2,000 National Guard members are expected to remain throughout May to help with security in Washington, a decision the National Guard Association disagreed with.
“This enduring requirement of having them around the city, I think it’s completely inappropriate at best, illegal at worst,” National Guard Association Chairman and Arizona Adjutant General Michael McGuire told the Washington Examiner on Friday.
The Washington Examiner contacted the National Guard for comment on Grennell’s identification but did not immediately receive a response.