(AP) — An Iowa man who was executed in Missouri for the 1987 murder of a 12-year-old girl has now been linked to an unsolved triple homicide three years earlier, investigators announced Friday.

New DNA evidence implicates Andrew Six in the 1984 bludgeoning deaths of 20-year-old Justin Hook Jr.; Hook’s fiancee, 19-year-old Tina Lade; and Hook’s mother, 41-year-old Sara Link, according to the Iowa Division of Criminal Investigation. Analysts did testing on evidence recovered from the inside of Lade’s jeans to develop a profile, which matched Six’s DNA.

Missouri authorities executed Six by lethal injection in 1997 for the kidnapping and murder of 12-year-old Kathy Allen. Six and his uncle kidnapped the girl from her family’s trailer in Ottumwa, a city in southeast Iowa, then slit her throat and dumped her body in northern Missouri.

Retired DCI supervisor Sam Swaim said that Six had long been a suspect in the 1984 triple homicide, but that investigators could not come up with enough evidence. He said that he was happy that scientific evidence has finally linked Six to the crime, but wishes Six had been caught earlier.

“I regret that we didn’t get that case solved. That would have saved Kathy Allen’s life,” he said in a phone interview.

Hook’s body was found outside his burned-out trailer in rural Drakesville, a sleepy town of 200 people near the Missouri border, in April 1984. When authorities tried to notify Hook’s mother at her home in Farmington, they learned that she was missing.

Days later, a farmer found her body on a hilly, wooded section of his home near Eldon, about 15 miles northeast of Drakesville. Two days later, police dogs found the body of Lade in a ravine a half-mile from where Link’s body was recovered. Investigators said all three had been killed by blows to the head, and that the deaths were related and probably happened around the same time.

The discovery of the bodies — day after day — shook a rural area that typically sees little violent crime. Friends said Hook had given Lade, of Ottumwa, an engagement ring days before their deaths on the birthday they shared, when she turned 19 and he turned 20.

“I’m glad they did the work that they’ve done,” said Cynthia Moyes of Coralville, the sister of Hook and daughter of Link. “It provided some closure.”