An inmate was found dead Wednesday in his Dakota County, Minn., jail cell, Sheriff Don Gudmundson said in a statement.

John Doyle, 40, of Spring Lake was unresponsive when his roommate tried to wake him up for breakfast. Efforts to revive him failed.

Doyle had been in custody since Oct. 11. He was arrested on outstanding warrants charging him with probation violations relating to felony terroristic threats and felony deprivation of parental rights.

Gudmundson said the initial investigation indicates Doyle died of natural causes, but a final determination will be made after results of toxicology tests are available.