She suffered severe injuries to her lower abdomen and legs, her femoral artery was cut and she was bleeding to death, Grey testified.
The testimony came on the first day of Shepherd's three-day jury trial for reckless endangerment and two other misdemeanors.
A trial for the other two men, Colton Raines, 23, and Robert Cole Boyer, 30, is scheduled for February.
All three are charged with misdemeanor counts in connection with Fujimoto's death on Aug. 21, 2011, while she was swimming in the reservoir, located seven miles east of Ogden.
According to a probable cause affidavit filed in 2nd District Court, the three men were boating near the Spring Creek Cove area of Pineview Reservoir at about 8 p.m. when their boat hit Fujimoto, who was swimming about 300 feet from shore. Shepherd allegedly told police that Raines was driving the boat at the time of the accident, but when they circled back to check on the woman, Shepherd took the wheel. Shepherd told police that Fujimoto told them she was OK, so the boaters left.
"They sealed her fate," Deputy Weber County Attorney Teral Tree said in opening statements. "Any chance she had for survival left with them when they sped off."
Fujimoto a U. lab specialist who was part of a research team that found a gene connected to breast cancer died soon after lake shore resident Vaughn Anderson rowed out to rescue her after hearing screams.
According to court documents, the boaters were questioned by wildlife officials later that day, but did not disclose that were involved in an accident. The men also allegedly wiped down the boat before it could be examined by police.
Defense attorney Glen Neeley said in opening statements that Shepherd did not talk to wildlife officials because he didn't know for sure if there was an accident, and they were initially told officials were looking for a blue boat, and his was white.
"It boils down to one question," Neeley told jurors. "The whole case is about knowledge. What did Skyler Shepherd know?"
Weber County Sheriff's deputy Paul Miya testified he was working marine patrol that day when he was called to the area on a report that a swimmer had been hit with a boat.
When he arrived, he found Anderson in a small rowboat, clinging to Fujimoto's hand.
"He was just shaking, trying to keep her above water," the officer testified.
Miya said it was not yet dark when he arrived, and he noticed discolored, darker water around Anderson's rowboat what he believed to be blood.
He said they pulled the woman out of the water into the Sheriff's Office boat, but she could not be saved.
Miya said he frequently saw Fujimoto swimming at Pineview Reservoir in the past, usually clad in a black wetsuit and bright pink swim cap, as she was on that day.
"She always swims along that shoreline," he said.
Watching the trial were members of Fujimoto's family, including her brother, Bryan Fujimoto, who said outside the courtroom that although it's been 15 months, they relive the accident every day.
"It's the outrage…" he said about the feelings he experienced watching the trial begin. "Others could have helped and did not do so."
He described his sister as a focused medical researcher who loved her work, and loved physical fitness. He said she had gone swimming in Pineview Reservoir at least 1,000 times in the last 15 years.
All three boaters are charged with a class A misdemeanor count of obstructing justice. In addition, Raines and Shepherd are charged with reckless endangerment, a class A misdemeanor, and failure to render aid, a class B misdemeanor.
The trial is set to continue Tuesday.