Adeline McLaughlin, an 84-year-old widow, was sexually assaulted and smothered with a pillow in 1983. Deborah Kisor, a 31-year-old mental patient, was assaulted and strangled four years later.
The killings were unsolved for years. St. Petersburg detectives submitted DNA for testing in the late 1990s, but had no luck.
Now, advances in DNA testing have given police the evidence to arrest the man they say killed both women: Tony Ables, a 51-year-old St. Petersburg man already convicted of two other murders and serving a life sentence.
"We do suspect there's a high probability" that Ables has killed others, said Maj. Michael Puetz.
For now, he faces a new charge of first-degree murder. Kisor's killing is not being prosecuted because she was involved with Ables, which complicates the case, police said.
Ables was first convicted of a murder in 1971, at age 16. He was sentenced to life in prison, but released 12 years later, and did construction work.
Five months after his release in 1983, police found McLaughlin's body in her apartment at Ten Eyck Hotel, a downtown retirement community.
Then, in 1987, children playing in the woods found Kisor's partly clothed body near Roser Park. She had been strangled.
In 1990, Ables was accused of beating Marlene Burns, his 48-year-old girlfriend, to death. In 1992, he was sentenced to life.
Last year, homicide detectives submitted DNA from various unsolved homicides to the Florida Department of Law Enforcement.
They recently received confirmation that the evidence recovered from McLaughlin's and Kisor's bodies matched with Ables, who had provided a DNA sample in 1992.