PLANO -- At the park that bears Ashley Estell’s name, there is renewed grief for a child’s murder that can’t seem to be solved. “It’s just heartbreaking, because you feel for her parents,” said Tiffany McCormack, a parent.

Friday, the Collin County district attorney admitted for the first time his office may have put the wrong man on death row for the 1993 murder of 7-year-old Ashley Estell. This was after DNA testing not available in the early ‘90s cleared Michael Blair.

“None of it ever linked Ashley Estell to Michael Blair, and vice versa,” said Phil Wischkaemper, Blair’s defense attorney.

In court, in papers obtained by Channel 8, prosecutors say they have another possibility: a man described only as "suspect number four", whom they found through their investigation to clear Blair.

This man raised suspicions with his odd behavior by doing, among other things, joining the Estell's church and buying a funeral plot as close as possible to Ashley's grave. A former doctor described him as a sociopath. He equipped his vehicle to look like a police car and he kept scrapbook of Ashley Estell items, as well as news footage of the case.

Perhaps most critically, unlike Blair, his DNA can't be excluded from Ashley Estell's shoe.

Suspect number four apparently died, however, more than 10 years ago, and prosecutors can't definitely tie him to the crime. Which means, some fear, Ashley's murder may remain unsolved.

For a crime that shook Plano to its core, and changed forever how parents like Tiffany McCormack watch their kids. “You know you would never want anything like that to happen. It’s every parent's worst nightmare,” said McCormack.

E-mail jbetz@wfaa.com