Patricia Dally of the Monroe County, Fla., Sheriff's Office said Wednesday the case is too old and the investigation would cost too much to continue.
But documents obtained by The Associated Press reveal new questions about the case.
Nelos Sills' death was ruled a suicide in 1965, when he was married to Betty Neumar. Although Florida investigators discovered that no autopsy was performed, Navy records show Sills may have been shot twice - not once as Neumar told police.
Florida had opened its investigation in June after Neumar's arrest in North Carolina in the 1986 death of her fourth husband, Harold Gentry.
Since her arrest, police have also begun to re-examine the deaths of her first child - Gary Flynn, whose 1985 death in Ohio was ruled a suicide - and three of her other husbands, though she faces no charges in those cases.
In the North Carolina case, Neumar, 76, is charged with three counts of solicitation to commit first-degree murder. Authorities now say she tried to hire three different people to kill Gentry in the six weeks before his bullet-riddled body was found in his rural North Carolina home.
Her attorney, Charles Parnell, did not return messages left Wednesday seeking comment. She was released last month after posting a $300,000 bond.
Neumar was working as a beautician in Jacksonville, Fla., in the mid-1960s when she met Sills, who was in the Navy.
On July 15, 1965, police found Sills' body in the bedroom of the couple's mobile home in Big Coppitt, Fla. Neumar told police they were alone, arguing, when he pulled out a gun and shot himself.
But new details have emerged in the case - all from Navy files.
When Monroe County investigators couldn't find records of the original case, they contacted Naval Criminal Investigative Service.
NCIS investigator Mark Barstow found Sills' military records, which contained details about the shooting.
The documents revealed that Sills may have been shot twice - not once as Neumar told police. One bullet from the .22-caliber pistol pierced his heart, while a second may have sliced his liver.
According to a Monroe County Sheriff's Office investigative report, the medical examiner said that without an autopsy, he would be unable determine if Sills had been shot once or twice. No autopsy was performed when Sills died.
Without knowing the number of gunshot wounds, there's no way to know if Sills' death was a suicide or homicide, according to the report.
Investigators planned to exhume Sills' body from an Ocala, Fla., cemetery for an autopsy. Then they discovered that a statute of limitations applied to the case, the records said.
In premeditated murder - or first degree murder - there was no statute of limitations. But Florida law sets a time limit on cases involving other categories of homicide, including involuntary manslaughter. And in Sills' case, they said, time had run out so they closed the case.
"We just didn't think this was premeditated murder because they had been arguing," said Patricia Dally, the lead investigator.
But critics asked how Florida police would know without a thorough investigation.
"They just dropped the ball," said Al Gentry, who spent 22 years trying to get North Carolina authorities to investigate his brother's murder. "They just wanted to bury this. You would think they would want to know what happened."
M. Dwayne Smith, a criminal justice professor at the University of South Florida, said despite the statute of limitations for non-first degree murders, "it seems there would need to be an investigation of the circumstances of the murder in order to determine what charging category would be appropriate."
Barstow, of NCIS, said Neumar received life insurance money in Sills' death, but he declined to elaborate. She also received life insurance money in the deaths of Gentry and her son, Gary Flynn.
Flynn and his sister, Peggy Sanders, were in the house the night Sills died. Sanders, who lives in Ocala, told North Carolina investigators she heard the argument and gunshot.
But Dally said she didn't interview Sanders because they just "didn't have the money to fly all over the state."
"I'm definitely curious about what happened. But there's a difference between curious and being able to prove something. Unfortunately, everyone here works around financial constraints. I don't know if we would be able to get the money to go in and do all this investigating," she said.
Georgia authorities recently closed their re-examination of the death of Neumar's fifth husband, John Neumar, saying they have no evidence she was involved. His family has criticized the police finding.
Authorities in Ohio have also said they were re-examining the 1950 death of Neumar's first husband, Clarence Malone. Malone was the father of Flynn, who was later adopted by Neumar's second husband, James A. Flynn.
It's unclear when Neumar met or married James Flynn. She told investigators he "died on a pier" somewhere in New York in the mid-1950s. She and Flynn had a daughter, Peggy, and his death is the only one officials are not reinvestigating.