Phoenix Police Sgt. Darren Burch called this one "a true whodunit."
He's talking about the April 24, 1987, murder of 34-year-old Diana Perkins.
"All we know is she was murdered inside her home, she was stabbed to death and we have nothing more to go on," said Burch.
Perkins lived in a home near 56th Avenue and Coronado. A mother of four, her 2-year-old son was there with her when she was stabbed to death.
She was a detention officer and her father was a retired MCSO deputy. Two of her sons are also now in law enforcement.
Diana's younger sister, Lattice, describes her as "just a really good person." She said more than 500 people showed up for her funeral, a testimony to the kind of person she was.
Diana graduated from Maryvale High School. After college, she followed in her father's footsteps and got into law enforcement.
Lattice said she would do anything for you. She didn't care what kind of situation you were in, she'd try to help. Diana loved going to church every week and loved spending time with her children.
Lattice said she also loved helping the homeless. Diana was described as quirky and Lattice said she liked to tell corny jokes.
And though decades have passed since she was killed, the pain of her family's loss is still fresh.
"No, it hasn't lessened at all," said Lattice.