Hans Peterson, 29, turned himself in to French authorities Aug. 6 on the Caribbean island of St. Martin after an arrest warrant was issued for him in Chicago. He is accused of fatally stabbing Dr. David Cornbleet in the dermatologist's downtown Chicago office in October.

Peterson, a U.S. citizen whose mother is French, obtained French citizenship in May while living on St. Martin, the Chicago Tribune reported. Peterson is being held in French-controlled Guadeloupe in the Caribbean.

The French government told U.S. authorities it is refusing the extradition request because of proof Peterson is a French citizen, according to Bernard Murray, a spokesman for the Cook County state's attorney office.

Murray said France typically doesn't extradite in cases where the suspect may face the death penalty. Peterson has not yet been charged in the case, so no potential penalty has been determined. The death penalty remains on the books in Illinois, though a state moratorium on carrying out executions has been in place since 2000.

Illinois' two U.S. senators, Dick Durbin and presidental candidate Barack Obama, have written to the French Embassy saying that Peterson should face prosecution in Cornbleet's death.

Cornbleet's son, Jon, has alleged Peterson killed the physician after being prescribed an acne medicine that he believed made him impotent. Police and prosecutors have not publicly commented on a possible motive.