Two murders stumped US police for 40 years. The key was sitting in a bathroom cabinet.

Police long suspected Jane Morton Antunez, right, and Patricia Dwyer were killed by the same person. Photo / San Luis Obispo County Sheriff's Office

With the illness marching through his body and his time running low, Arthur Rudy Martinez turned himself in.

It was April 2014. Twenty years earlier, Martinez had escaped from a Washington state prison where he was serving a life sentence for robbery and rape convictions. Running from authorities, Martinez headed south, where he slipped into an alias and lived under the radar around Fresno, Calif.

The fugitive's true identity may have never come out if he had not been diagnosed with terminal cancer.

According to law enforcement, Martinez returned to Washington and gave himself up on April 30, 2014. He knew he would receive medical treatment in prison. Within two months, he was dead at 65.

But law enforcement was not done with Martinez. On Wednesday, Ian Parkinson, the sheriff of San Luis Obispo County, California, held a news conference to announce his office had solved two open homicides from the late 1970s.

Using updated DNA techniques, including genealogical research, investigators have tied Martinez to the two crimes.

But as the San Luis Obispo Tribune reported on Wednesday, solving the decades-old killings also hinged on something so common that it's found in nearly every household — a cluttered bathroom medicine cabinet.

Jane Morton Antunez was found first.

According to a news release from the San Luis Obispo County Sheriff's Office, the 30-year-old was discovered in the back seat of her car on an isolated dirt road in Atascadero, California, on the afternoon of November 18, 1977. Her throat had been slit, and she had been sexually assaulted. The night before, Antunez had been traveling to her best friend's house but never showed up.

Less than two months later, on January 11, 1978, Patricia Dwyer, 28, was discovered dead on the floor of her home in Atascadero. She had also been sexually assaulted and stabbed in the chest with a knife from her kitchen.

Even though they shared some common friends and both were known to hang out at an Atascadero watering hole called the Tally Ho Bar, very little seemed to connect the two women. But as the Tribune reported, investigators at the time believed Antunez and Dwyer had been attacked by the same person. Both had been sexually assaulted, and both were found with their hands bound behind their backs.

One name that did briefly flash through the investigation was Arthur Rudy Martinez. In early 1977, Martinez had been paroled to the area after serving a decade-long prison sentence for attempted murder and rape in Fresno, the Tribune reported. According to authorities, Martinez worked at a local welding shop at the time of the killings.

But police couldn't find any evidence directly linking Martinez to the murders. The lone witness who saw a man near Antunez's car on the night of her death was not even shown Martinez's picture.

Shortly after the crimes, Martinez left California for Washington, where, by the end of 1978, he was convicted of a number of robberies and two rapes. He died in June 2014, leaving no indication of his part in the unsolved slayings in California.

With DNA breakthroughs in mind, investigators with the San Luis Obispo County Sheriff's Office in 2005 submitted DNA collected from the 1977 and 1978 crime scenes for analysis. It conclusively showed that Antunez and Dwyer had been killed by the same attacker. But the analysis failed to point authorities to that murderer.

As Parkinson told reporters Wednesday, the county found money in 2016 for a cold case detective for the sheriff's office. The job went to a detective named Clint Cole, who in 2017 began reviewing unsolved murders from the late 1970s.

But the DNA analysis still didn't match anyone in the statewide system, Parkinson explained on Wednesday, so Cole submitted the suspect's DNA profile to the Justice Department's familial DNA search team in Richmond, California, in March 2018. Its results indicated that Antunez's killer was related to an inmate then serving charges for a different offence.

Investigators eventually determined the inmate with a familial match had a relative living in San Luis Obispo County at the time of the murders: Martinez.

But with the suspect long dead, investigators were faced with another problem: They needed DNA from Martinez to compare with the crime scene sample.

According to the Tribune, investigators tracked down a girlfriend who had lived with Martinez when he was on the lam before 2014 in the Fresno area. Remarkably, the woman went into her medicine cabinet and pulled out an old razor Martinez had used.

That razor was tested and came back as a DNA match to the material taken from the crime scene.

Additionally, investigators contacted the witness who had seen a man near the Antunez crime scene.

"Over the years, this witness had seen many photos of possible suspects, and at no time was able to make an identification," Parkinson told reporters Wednesday. "She immediately identified Martinez as the suspect she saw some 40 years later."