The vast majority of dead animals that have been found in the Gulf of Mexico -- 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. Lt. Donald Armes of the Mississippi Marine Patrol checks shrimp boats for compliance with turtle-exclusion regulations on the Mississippi sound.
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, waiting for scientists to begin the process of determining what killed them.
This Kemp's ridley sea turtle, found floating in the Mississipi Sound on June 18, is one of hundreds of dead creaures collected along the Gulf Coast since the Deepwater Horizon oil rig exploded.
The bright orange X spray-painted on its shell was proof that had been counted as part of the Gulf of Mexico's ongoing "unusual mortality event."
Dr. Brian Stacy, a veterinary pathologist, estimates that he has dissected close to 1,000 turtles over the course of his career.
Under Dr. Stacy's practiced knife, the specimen began to reveal its secrets: First, as the breastplate was lifted away, pictured, a mass of shriveled organs in the puddle of stinky red liquid that is produced as decomposition advances. Then, the fat reserves indicating good health. Later, when Dr. Stacy sliced open the esophagus, the most revealing clue: a morsel of shrimp, the last thing the turtle ate.
The efforts to finger a culprit -- or culprits -- amount to a vast investigation the likes of which "CSI" has never seen.
The trail of evidence leads fom marine patrols in Mississippi, where more than half the dead turtles have been found, to a toxicology lab in Lubbock, Tex., to this animal autopsy room at the University of Florida in Gainesville.
Jennifer Cole, a doctoral student at the Institute of Environmental and Human Health at Texas Tech University, sliced a precious chunk of living dolphin tissue into .3-millimeter sections.
Ms. Cole was studying cytochrome P450 1A1, an enzyme that breaks down hydrocarbons. Tissue samples are one of the only ways to learn more about toxins in marine mammals and sea turtles, whose protected status limits the type of studies that can be done -- researchers cannot do experiments to determine how much oil the animals can withstand.
Dr. Ronald J. Kendall, director of the Institute of Environmental and Human Health at Texas Tech University, demonstrates an oil-absorbing fiber developed by Assistant Prof. Seshadri Ramkumar.
Oil is measured on an unfertilized chicken egg in developing criteria to study the effects of oil on the fertilized eggs of animals affected by the oil spill.
A graph compares the analysis of chemicals in crude oil found off the Louisiana and Alabama coasts.
A blue crab called Lefty is acclimated in a new tank before crude oil from the Gulf of Mexico is added.
The piece of shrimp that Dr. Stacy found lodged in the turtle's throat pointed to shrimpers. A turtle is normally not quick enough to catch shrimp, unless, of course, it is caught in a net with them. Here, a shrimper on board the Lucky Baby, which was boarded by Marine Patrol officers on a routine compliance check.