A Suffolk forensic pathologist stood by her conclusion that a young Islip man died from being bludgeoned, choked and buried alive in a watery grave, but conceded during cross-examination Friday that the autopsy could tell her only so much.

Dr. Stephanie Horowitz, a deputy medical examiner, finished her third day on the witness stand at the trial of Thomas Liming, 23, of Islip, in state Supreme Court in Riverhead.

Liming is charged with second-degree murder, accused of killing his former high school friend Kyle Underhill, 18, in 2011 in marshy woods off Brook Street in Islip.

During questioning by defense attorney Joseph Corozzo of Manhattan, Horowitz said it was impossible to say if any of the three phases of the attack was more responsible for Underhill's death.

"They combine in their effects," she said. "I can't tell for certain what order these things happened in."

Earlier this week, she said Underhill suffered brain bleeding from at least 15 blows to the head, perhaps with a shovel. Friday, she said she couldn't be certain it was a shovel.

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She also said Underhill was choked hard enough to break cartilage in his neck and to cause pinpoint hemorrhages in his eyes and elsewhere. And plant matter and other debris in his lungs showed he was still breathing when he was buried in a grave filled with muddy water the night of Nov. 16, 2011.

Horowitz said she couldn't tell how long the attack took. She said Underhill's heart stopped beating not long after the beating, because she otherwise would have expected to find more blood inside his skull from the torn veins in his brain.

But she couldn't say when Underhill took his final "agonal gasps" in the grave. She noted that Underhill's lungs were heavier than normal, a sign of "a relatively slow death."

During questioning by Assistant District Attorney Raphael Pearl, Horowitz dismissed some of Corozzo's suggestions about the attack, such as whether it took a long time or if some injuries came from falling onto rocks or stumps.

"Many things are possible if you use a lot of imagination, but they're not necessarily likely," she said.