GAINESVILLE, Fla. — The Kemp’s ridley sea turtle lay belly-up on the metal autopsy table, as pallid as split-pea soup but for the bright orange X spray-painted on its shell, proof that it had been counted as part of the Gulf of Mexico’s continuing “unusual mortality event.”

Under the practiced knife of Dr. Brian Stacy, a veterinary pathologist who estimates that he has dissected close to 1,000 turtles over the course of his career, the specimen began to reveal its secrets: First, as the breastplate was lifted away, a mass of shriveled organs in the puddle of stinking red liquid that is produced as decomposition advances. Next, the fat reserves indicating good health. Then, as Dr. Stacy sliced open the esophagus, the most revealing clue: a morsel of shrimp, the last thing the turtle ate.

“You don’t see shrimp consumed as part of the normal diet” of Kemp’s ridleys, Dr. Stacy said.

This turtle, found floating in the Mississippi Sound on June 18, is one of hundreds of dead creatures collected along the Gulf Coast since the Deepwater Horizon oil rig exploded. Swabbed for oil, tagged and wrapped in plastic “body bags” sealed with evidence tape, the carcasses — many times the number normally found at this time of year — are piling up in freezer trucks stationed along the coast, waiting for scientists like Dr. Stacy, who works for the National Oceanic and Atmospheric Administration, to begin the process of determining what killed them.

Despite an obvious suspect, oil, the answer is far from clear. The vast majority of the dead animals that have been found — 1,866 birds, 463 turtles, 59 dolphins and one sperm whale — show no visible signs of oil contamination. Much of the evidence in the turtle cases points, in fact, to shrimping or other commercial fishing, but other suspects include oil fumes, oiled food, the dispersants used to break up the oil or even disease.