Dr. Walter Palmer Surfaces ... Contacts Investigators

Dr. Walter Palmer -- the dentist who gunned down Cecil the Lion -- has resurfaced and contacted authorities after days of hiding ... TMZ has learned.

Officials for U.S. Fish and Wildlife Service tell us a rep for Dr. Palmer contacted them late Thursday.

We're told Dr. Palmer is cooperating with the investigation into Cecil's death, which focuses on an international law governing hunters who move their trophies from one country to another.

Fish and Wildlife have been looking to speak with Dr. Palmer as it conducts its investigation into the killing of Cecil. The U.S. Dept. of Justice is also investigating.