(AP) — Nebraska officials investigating the death of an Iowa man are awaiting autopsy results.

35-year-old Matthew Ahlsten, of Sioux City, died Sunday morning. He was a passenger in a vehicle pulled over by a Nebraska State Patrol trooper. The reason for the traffic stop hasn’t been disclosed.

Patrol Capt. Paul Hattan says Ahlsten “did die at the scene of that traffic stop, and obviously it’s under investigation by the Dakota County Sheriff’s Office as a result of that in-custody death.”

Police are not releasing any other information at this time.