(CNN) -- A Kentucky census worker who was found dead in September committed suicide and staged the scene to look like a homicide, authorities said Tuesday.

The body of William E. Sparkman Jr., 51, was found September 12 near a cemetery in southeastern Kentucky's Clay County. He was wearing only socks.

"A thorough examination of evidence from the scene, to include DNA testing, as well as examination of his vehicle and his residence, resulted in the determination that Mr. Sparkman, alone, handled the key pieces of evidence with no indications of any other persons involved," Kentucky State Police said.

Sparkman's wrists were bound with duct tape, and a rope around his neck was tied to a tree, but his body was touching the ground, authorities said. He had "Fed" written on his chest in black ink.

However, Sparkman's wrists were loosely bound in front of his body at shoulder width apart, allowing for "considerable mobility," said Kentucky State Police Capt. Lisa Rudzinski.

He was also in contact with the ground, "almost on his knees," she said.

"To survive, all Mr. Sparkman had to do was stand up."

Lividity on the body -- marks made as blood stops pumping and settles in areas of the body -- showed that Sparkman died in the same position, Rudzinski said.

His glasses were taped to his head, and that tape was underneath tape that held a rag in his mouth, she said.

"Mr. Sparkman had extremely poor eyesight" and so would have needed his glasses secured, Rudzinski said.

But the most compelling evidence came from the fact that Sparkman had obtained $600,000 in accidental-death insurance, which would not have paid in the event of a suicide, as late as May, she said.

In addition, he told a "credible witness" of his plans to commit suicide and stage the scene to make it look like he was slain because he worked for the federal government. The details were consistent with how Sparkman died and was found, Rudzinski said.

The witness did not take action after Sparkman shared his plans out of a belief that he would not follow through, authorities said.

"It was learned that Mr. Sparkman had discussed recent federal investigations and the perceived negative attitudes toward federal entities by some residents of Clay County," Kentucky state police said in a statement.

Police believe that Sparkman's primary motive in staging the scene was to ensure that the insurance would be paid, Rudzinski said. His motive for committing suicide or any secondary motives might never be known, she said, as Sparkman left no note.

"We don't know what Mr. Sparkman was thinking or why he ultimately committed this act," she said.

Autopsy results showed no evidence of any cancer or terminal illness, officials said, although it was reported that Sparkman had previously had lymphoma. Police would not say who the beneficiary of the insurance was.

Forensic analysis of the writing on Sparkman's chest showed that he had written it himself, Rudzinski said. Analysts found ink dots, made by writers on completing a letter, at the top of the letters, rather than at the bottom -- as would be expected if someone had made the writing on Sparkman. Despite a search by authorities, the black felt pen used for the writing has not been found.

Police do not believe that anyone assisted Sparkman, she said.

Sparkman had told the witness, whom police declined to name, that he intended to dispose of some of his personal effects, including his laptop computer and other items. Police have not found those items, Rudzinski said.

Toxicology tests showed that Sparkman was not drugged or under the influence of any substance, she said. The red rag removed from his mouth was similar to those found in his pocket and at the scene.

DNA testing of the rags and the rope used in creating a ligature on Sparkman's neck, as well as 7 feet of discarded rope discarded near his body, found only Sparkman's DNA, she said.

The police investigation is still open, and additional test results are expected in the next two to three weeks, authorities said.

Authorities met with Sparkman's son and told him of their findings before publicly releasing them.

"Our hearts go out to him," Rudzinski said. "He still lost his father at the end of the day."

She would not say whether his son accepted the findings, saying she did not want to speak for the family.