The young Islip man pulled from a watery grave four years ago suffered so many different kinds of injuries that any of the three ways he was attacked could have caused his death, a Suffolk deputy medical examiner testified Thursday.

Using three dozen graphic autopsy photos projected on a screen, Dr. Stephanie Horowitz described the results of a relentless attack before Kyle Underhill, 18, was buried in a marsh off Brook Street in Islip on Nov. 16, 2011. She testified at the trial of Thomas Liming of Islip, now 23, a former high school friend of Underhill.

Both Liming and Underhill's relatives avoided looking at the screen.

Underhill suffered three general types of injuries, Horowitz said during questioning by Assistant District Attorney Raphael Pearl:

He was hit at least 19 times in the head with an object -- perhaps a shovel -- with such force that veins in his brain ripped, Horowitz said.

He was suffocated both by having his neck compressed with enough force to break some cartilage in his neck and by having his chest compressed -- possibly by someone kneeling on it while beating his head, she said. He also had several broken ribs.

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And after his attacker jammed two sticks, each 3 3/4 inches long, into his mouth, Horowitz said he was buried alive in the muck. As he died, he inhaled plant material, mud and other particles, she said.

Any of these three actions alone would have caused his death, but all three happened at about the same time and all were responsible for his death, Horowitz said.

Defense attorney Joseph Corozzo of Manhattan has argued that Liming was fending off an attack by Underhill in the woods. In her opening statement, Assistant District Attorney Kathleen Kearon said the "sheer, massive overkill" made any suggestion of self-defense illogical.

Horowitz said Underhill had some defensive wounds on one arm, as if he were fending off blows to his head. There were no injuries to his hands or knuckles, she said.

During cross-examination in State Supreme Court in Riverhead, Horowitz rejected alternate theories Corozzo suggested for how Underhill got so many severe injuries. He argued, for example, that it's possible that if Underhill fell or was pushed onto rocks or tree roots, he would have gotten more than one blow to the head at the same time.

Horowitz said that was unlikely because a head is curved, and Underhill had bruises, torn skin and scrapes from blows on the front, back, top and left sides of his head.

Horowitz told Pearl that Underhill had no alcohol in his blood and no illegal drugs in his system. She told Corozzo that being submerged in muddy water for a couple of days after death would not have diluted his blood or other body fluids.