Colton Raines, 23, and Robert Cole Boyer, 30, were also charged with obstructing justice.
Raines, who was driving the boat when it hit swimmer Esther Fujimoto, 49, was additionally charged with reckless endangerment and failure to render aid the same charges of which Shepherd was convicted.
But defense attorney Greg Skordas said the case against Raines will not mirror Shepherd's.
"Their cases have been separated for a reason," he said, adding there is still time before the February trial to consider the possibility of a plea deal.
"Certainly, there are always reasons to negotiate," said Skordas, who represents both Boyer and Raines. "But right now it appears we're going ahead to trial."
According to testimony during Shepherd's trial in 2nd District Court, the three were boating near the Spring Creek Cove area of the reservoir at about 8 p.m. on Aug. 21, 2011, after drinking with friends earlier in the day.
Raines was driving when the boat hit Fujimoto, but Shepherd took the wheel and circled back to check on the woman. He told police that Fujimoto grunted and said she was OK, so they left her in the water.
But Chief Medical Examiner Todd Grey testified that Fujimoto had severe injuries to her lower abdomen. Her legs were "chopped to pieces," her femoral artery had been cut and she was bleeding to death.
She died soon after a lakeshore resident who heard her screams rowed out to help her.
Trial for Raines and Boyer is set to begin Feb. 11 before Judge Ernie Jones.