A Calumet City, IL, police officer died of an apparent medical emergency early Monday while on duty in the south suburbs.

Officer Adam Zieminski, a 22-year department veteran, was transporting a detainee to the Markham Courthouse when he suffered the medical emergency, according to a statement from Calumet City, the Chicago Sun-Times reports.

The detainee alerted nearby Cook County sheriff’s officers, who responded but were unable to revive Zieminski, 49, the city said in its statement.