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MEMPHIS, Tenn. — Autopsy results for three men found dead at Reelfoot Lake in northwest Tennessee in January back a survivor’s account of the shooting, officials said.

Tommy Thomas, district attorney for Obion and Weakley counties, said his office received the autopsy reports on Chance Black, Zachary Grooms and David Vowell, the man who allegedly killed them.

The district attorney’s office said it found “no basis for criminal charges” in the incident, but per office policy, would refer the case to the Obion County grand jury in June.

The cause of Vowell’s death could not be concluded, but the medical examiner said it appeared that he died either of drowning or hypothermia.

Vowell also had a non-fatal bruise on his head, according to the medical examiner. That was consistent with a witness’s account of fighting him off, the district attorney said.

Black, 25, and Grooms, 26 were found shot to death in a duck blind at the lake Jan. 25. Vowell, 70, was charged with two counts of murder in their deaths and was the subject of a manhunt, but he was found dead at the lake several days later.

A third man, Jeff Crabtree, survived the shooting and told investigators what he witnessed. The district attorney’s office said autopsy findings were consistent with his account.

According to Crabtree’s account in documents released by authorities, Black, Grooms and Crabtree were in a duck blind when Vowell entered their blind and asked if he could hunt with them. He then shot two of the men in the chest with a shotgun. Crabtree fought with Vowell and escaped.

Vowell was last seen standing in the water, and was found face-down in the water five days later after flood waters receded. The medical examiner said it was unclear whether he had been pushed into the water or fell as he tried to escape.

Vowell’s autopsy found no evidence of brain abnormality or mind-altering substances, a fact that leaves Thomas with lingering questions.

Thomas said there was “nothing to indicate why this gentleman would have acted irrationally. But I’ve been in this job long enough to know that nothing really surprises me anymore.”