The discovery comes on the same day a state funeral was held to honor Robredo, the Philippines GMA News reported Tuesday.
Robredo, the plane's pilot and co-pilot were killed August 18 when the Piper Seneca crashed off the coast of Masbate City on a flight from Cebu to Naga City.
A deputy who survived the crash managed to escape the plane before it sank.
President Benigno Aquino III delivered the eulogy at Robredo's funeral and conferred the Philippine Legion of Honor with the rank of chief commander on the late government official, The Philippine Star reported.
Robredo is survived by his wife and three children.