YULEE, Fla. -- A 37-year-old man found with his parents' missing SUV hours after the couple was found dead in their Amelia Island home earlier this month was charged Wednesday with two counts of murder.

Nassau County deputies said 75-year-old Richard Larkin and his 73-year-old wife, Myra, were found dead April 18 when someone went to their home to check on the couple after they failed to show up for a conference.

According to the sheriff's office, the victims were found in different rooms of the home and died of blunt force trauma. Investigators believe the couple had been dead for several days.

After visiting the crime scene, Sheriff Tommy Seagraves called it "One of the most violent scenes that I have even witnessed in my law enforcement career."

Because there were no signs of forced entry and because the two victims were found in different parts of the home, investigators quickly announced that the couple's son, Gregory Larkin, 37, was a person of interest in the case.

He was found that night in a hotel at Jacksonville International Airport with the missing SUV parked outside.

Larkin was initially arrested and charged with auto theft and invalid driver's license and was ordered held on $200,000 bond. Thursday morning, Seagraves explained the evidence that led them to charge Larking with two counts of murder.

Seagraves said several pieces of evidence -- including his mother's blood on Gregory Larkin's clothing -- allowed them to upgrade the charges.

"He had person items on him when he was found that belonged to the victims," Seagraves said. "We do have what we believe is the weapon, and that is also being analyzed at the FDLE lab."

Seagraves said they were still not sure of a motive for the slayings, although there were reports of financial problems in the family.

Gregory Larkin and three other siblings ran a family-owned dive shop in Costa Rica, but Gregory Larkin had returned to the United States in January and had been living with his parents.

Gregory Larkin told investigators he had been in Mexico since Easter Sunday and had just returned to town, which evidence He said he was robbed while in Mexico and the keys to the family's SUV were taken, so he had to get a room at an airport hotel after returning to town Saturday.

Seagraves said travel documents verify that Larkin did make that trip, so they believe he killed his parents before he left town and their bodies were not found for a week.

"The last time that we do know that the Larkins were alive was on April 11," Seagraves. "(Greg Larkin) flew out of JIA -- Jacksonville International Airport -- there on April 12."