A Dallas housewife on death row for stabbing her two sons to death has undergone a shocking transformation revealed in an upcoming documentary.

Darlie Routier laid bare her first person account of the horrific 1996 murders in a two-hour program by ABC's 20/20 airing on Friday.

Routier has spent the past two decades protesting her innocence, maintaining that an intruder entered the family's home and attacked her sons, five and six, while they were asleep in front of the TV.

Prosecutors managed to convince a jury that the mother had fabricated the account. She was convicted of murdering the younger son, Damon, when she was 27 years old in 1997.

She was never tried for the murder of her eldest son Devon, as prosecutors wanted the option to pursue a second indictment should the first fail in court.

Routier's appearance has changed dramatically over her time behind bars, as she transitioned from a lithe blonde into a heavy-set brunette.

Dallas housewife Darlie Routier has undergone a shocking transformation over her the past 20 decades she's spent on death row for killing her two young sons. The now-48-year-old shares her own account and maintains her innocence in a 20/20 documentary airing this week

But in an interview from prison she still insists she is innocent, saying: 'I cannot actually believe they're doing this to me when I didn't do this. I didn't kill Devon and Damon.'

Along with Routier's account, the documentary includes a video shown by prosecutors during the trial of the mother having a party at her children’s gravesite and other evidence presented by the state that points to her as the killer.

It also shows the defense questioning the state's theory of motive and the characterization of Routier, her current defense team's alternative theories that the jury may not have fully considered and an interview with Darin Routier, the defendant's ex-husband.

Darin Routier talks about the events leading up to her arrest, including the night of the murders, and lays out why he still believes she is innocent.

Prosecutors contended that Routier was angry over money problems and the burdens of motherhood (pictured with her two eldest sons)

Darlie, a native of Altoona, Pennsylvania, met her future husband, Darin Routier, in Lubbock, Texas, when she was a teenager and he was the assistant manager of a restaurant. The couple dated for several years before marrying in 1988.

They settled in the Dallas area, where Darin Routier's business testing circuit boards took off a few years later.

The couple spent their newfound wealth - as much as $500,000 a year - on a Jaguar, cabin-cruiser, vacations and an upscale home replete with a fountain in the front yard and hot tub in back.

But with the new purchases came hefty bills, and by May 1996 the Routiers owed $10,000 in back taxes, $12,000 on credit cards and two months of mortgage payments.

During the trial, prosecutors contended that Routier was angry over money problems and the burdens of motherhood, and that she slashed herself to cover the crime.

The prosecution repeatedly showed the court video of Routier giggling and spraying Silly String on her sons' graves on what would have been Devon's seventh birthday.

She was arrested just days after the graveside celebration, which her mother, Darlie Kee, said was the family's way of dealing with their loss, as Dallas News reported.

Routier shows severe bruising on her right arm after the stabbing, which she blamed on an intruder

It took the jury 10 hours spread over two days to convict Routier of capital murder.

Despite being found guilty and condemned to die, Routier' mother, ex-husband, family and friends have stood by her over the years, insisting that she was innocent.

Routier's supporters often point to a bloody sock that was found in the alley about 75 yards from the family's home, with bloodspatters from the two children, as well as a bloody fingerprint that was found on a table near the body of one of the children.

Cooper, Routier's lawyer, said when the fingerprint, known in the case as 85-J, was tested, no DNA could be extracted from it because it has degraded over time.

Routier's case was featured on the multi-part docuseries The Last Defense exploring the failures of the American justice system, which aired on ABC over the summer.

Her sole surviving son, Drake, now in his early 20s, was diagnosed with leukemia two years ago, but the disease is said to be in remission.

For now, Routier, aged 48, remains on death row in Gatesville Prison, Texas, and is one of six women sentenced to death in the state.

No date has been set for her execution as the case continues to go through the state's appellate court system.

The last woman to be put to death in Texas was Lisa Coleman, 38, who was given a lethal injection in 2014 for the starvation death of her girlfriend's son.