Grennell, 26, from Marcellus, New York, was found unresponsive in his Washington, D.C. hotel room Thursday by his roommate who tried to revive him before calling 911, a local Syracuse news outlet reported.
Metropolitan Police are still investigating the death, but foul play is not suspected, a New York National Guard spokesperson said.
“Joint Task Force District of Columbia is sad to confirm the death of a National Guard member serving with the U.S. Capitol security mission due to an apparent medical emergency. The individual was not on duty at the time, and the incident is under investigation,” the National Guard said in a statement.
Grennell was a part of the massive security effort assigned as the U.S. Capitol following the Jan. 6 riot.
Earlier this week the Pentagon ordered that 2,000 troops would remain in Washington through May for additional security purposes at the request of Capitol Police.
“This decision was made after a thorough review of the request and after close consideration of its potential impact on readiness,” Pentagon press secretary John Kirby said following the announcement.
The troops are expected to remain until May 23.
Some lawmakers were frustrated by the Pentagon’s announcement following reports of Guard members falling ill and poor conditions during their deployment.
“They have proudly answered the call, served our country,” Rep. Jack Bergman, R-Mich., wrote in a letter last week to the chief of the National Guard Bureau, following reports of 50 service members having gastrointestinal issues due to inadequate food.
“Our troops don’t demand a five-star resort or expensive food, but at a minimum, they deserve meals that are safe to consume,” he continued, adding, “It’s time to get our troops home to their families.”