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Kera Williams,
Skyler Shepherd covers his face during his trial in 2nd District Court in Ogden on Monday, Dec. 10, 2012.

OGDEN — A trial is under way for one of three men accused of riding in a motorboat when it severed a swimmer's legs and killed the woman, a University of Utah scientist.

Prosecutors laid out their case Monday against Skyler Shepherd, 22, the boat owner who told police another defendant was driving when it hit Esther Fujimoto on Aug. 21, 2011, at Pineview Reservoir, seven miles east of Ogden.

Shepherd told authorities he took the wheel to circle back to the swimmer. The boaters have said they left the woman in the water after she reported she was OK. A medical examiner determined Fujimoto died from propeller wounds.

Fujimoto, 49, was part of a U. team that identified a breast cancer gene. More recently, she was seeking a cure for cerebral palsy. Her family has sued the three men for wrongful death, claiming in court records they were drinking and smoking marijuana when they hit her several hundred feet from shore.

The defendants' lawyers counter that Fujimoto was negligent for swimming in open water.

A separate trial will be held in February for Colton Raines, 23, and Robert Cole Boyer, 30. All three defendants face misdemeanor charges of obstructing justice, reckless endangerment and failing to render aid.

Shepherd's trial got under way Monday amid speculation he might blame another defendant for the fatal accident. His lawyer, Glen Neeley, raised that possibility in a court motion seeking a separate trial for Shepherd. Prosecutors didn't object.