Teens' sinister plot to kill their parents: Sixteen-year-old boy murders 17-year-old girlfriend's hardworking mother after their friend tried to stab her sleeping mom in bed

An upcoming true crime documentary is set to delve into a sinister plot by four teens who made a pact to kill their parents with devastating results.

Susan Bailey, 43, was found stabbed to death with her throat slit at the top of the stairs in the family home in Roanoke, Texas.

Her two children - Jennifer, 17, and David, 13 - were nowhere to be found until police caught them attempting to flee alongside Jennifer's 16-year-old boyfriend, Paul Henson Jr.

It would later transpire that the young couple had planned to murder the single mom, who had been working two jobs to provide for her kids, as part of a twisted pact with a fourth teen Merrilee White, 14.

Here, FEMAIL has laid bare the sordid details as Oxygen's Snapped: Killer Couples gets set to unravel the case.

The chilling tale began to unravel on September 26, 2008 when Susan failed to show up for work at a retail store.

Her colleagues were 'concerned' by her absence and her manager attempted to call her multiple times because it was unusual for the mom-of-two not to check in.

The emergency contact on file for Susan was her mother, who lived in Minnesota, but she too was unaware of her whereabouts.

Susan's concerned mom then began to call around - including to grandchildren Jennifer and David - but could not get hold of any of the family.

She eventually contacted Roanoke Police who headed over to the house in the upscale neighborhood to carry out a welfare check later in the evening.

Officers initially reported that there was nothing out of the ordinary - the car was not in the driveway, nobody answered the door and there was nothing to indicate forced entry.

The police had no immediate concerns until a cop in South Dakota stopped Susan's car a few days later and did not believe the testimony from its young occupants. 

He alerted Roanoke Police who then decided to return to the Bailey home - and, after gaining entry, officers made a series of shocking discoveries.

Susan's lifeless body was found lying on the floor in a pool of blood having been killed in a frenzied knife attack.

She had suffered 26 different wounds - having been stabbed multiple times and had her throat slit with blood splattering across the walls.

And, in another bizarre twist, police also found a bowl of poisoned chocolate pudding in the fridge, hunks of recently-cut hair, cell phones submerged in water and a bathtub rigged for an electrocution.

The murder was described as 'extremely brutal, extremely violent' by prosecutor for Denton County Jamie Beck.

Susan's kids - along with Paul - who had been stopped using the mom-of-two's car were brought in and their sinister plot soon began to unravel.

Jennifer and Paul had started dating during high school, but Susan had disapproved of her daughter's boyfriend.

She grew suspicious of Paul's influence - and despite Jennifer's hopes of attending art college in Dallas her grades started to slip and her behavior worsened.

Around the same time Paul had also befriended 14-year-old Merrilee and began dating both girls at the same time.

The trio then entered into a three-way sexual relationship.

'They believed they had been together in other lives. He liked to have sex with both girls and watch them have sex with each other,' crime author Donna Fielder told Oxygen. 

Merrilee's mother, much like Susan, also took a dim view of her own daughter's liaisons.

And, with tensions between the girls and their parents increasing, Jennifer, Paul and Merrilee hatched their gruesome plan.

It transpired that the trio, along with Jennifer's younger brother David, had all agreed to kill their parents, steal their cars and credit cards, and flee to Canada.

Merrilee had attempted to strike first and on September 23 her mother woke to find her daughter standing over her with a large butcher's knife.

Her mom was able to call police and the young girl was taken to a juvenile detention center.

The following day Paul's father reported his son as a runaway and informed police that he had also got his hands on his .22 caliber pistol.

It was not long before he, along with Jennifer and David, struck and killed Susan together - having made set up multiple plans to kill her, with one plan being 'to electrocute her in the shower,' according to Beck.

But the group of teens did a poor job of covering their tracks - after leaving locks of Paul's freshly-cut hair at the scene along with bandanas covered in Jennifer and David's DNA, which the brother-sister duo had worn at the time of the killing. 

The officer from South Dakota found them three days later loitering outside a closed gas station at 3.30am.

Their story changed constantly and the truth eventually came out before they were tried.

All three were under 18 at the time of the murder and so were not eligible for the death penalty.

Jennifer and Paul both pleaded guilty and were each sentenced to 60 years in prison. David was charged as a juvenile.