They then watched four Twilight vampire films and had sex as they “revelled”.
The full details of the horror killing can be reported for the first time today after judges at London’s Court of Appeal ruled the evil pair could be named.
The identities of the couple, dubbed the ‘Twilight killers’, could not be reported throughout a trial at Nottingham Crown Court last year because of their age.
But restrictions on naming them were lifted by three judges today, who also reduced their 20-year minimum custodial terms to 17 and a half years each.
Edwards and her partner, likened to Bonnie and Clyde in court, slashed their victims through their voice boxes to stop them screaming during the attack last April.
Police found the pair’s bodies in their blood-spattered bedrooms in Spalding, Lincolnshire, two days after they were slaughtered by the couple.
The court was told the teen sweethearts were like “a time bomb waiting to go off” after they became “inseparable” in the weeks before the killings.
Edwards, now 15, was found guilty of murder last October after a five-day trial, while Markham, also now 15, pleaded guilty to Elizabeth and Katie’s murders.
“The killings were brutal in the form of executions and both victims, particularly Elizabeth Edwards, must have suffered terribly in the last minutes of their lives.”
The Crown Court had heard how the boy used a kitchen knife to stab both victims in the neck after attacking them as they slept at their home.
Elizabeth was stabbed eight times – including five times in the hands as she desperately tried to defend herself. One of the two blows to her neck almost completely cut through her windpipe.
Put off by the smell of blood, the teenager planned to wait in the bathroom as their heinous plot unfolded, the court was told.
She later told police she did not have the “mental or physical” strength to commit murder herself but was “okay” with what happened.
But she came into the bedroom after she heard noises and became concerned her boyfriend was being overpowered.
She told police: “He was on top of her with a pillow over her head. I think I heard her say ‘get off me’. There was blood on her and on the bed, there were four blood spatters on the wall and he told me to shut the door.
” All I could see was her shoulder and arms. She was struggling.
“She reached out her hand so I grabbed it and kind of held it. As I realised it was her hand I instantly drew my hand back and got into a cradle position.
“I sat on the floor next to the door and said to myself: ‘breathe’, as I was about to have a panic attack. My legs were shaking.
“Then I walked back and forth and said: ‘It’s going to be OK, keep calm. It’s going to be over soon’. After about ten minutes of putting his weight on her she was dead.
“She had kind of gone limp and wasn’t struggling anymore but she was still making gurgling sounds. I think I said: ‘Is she dead?'”
Markham then calmly checked the victim’s pulse before moving on into the next bedroom. He took his shoes off so he wouldn’t make a noise, the court heard.
Katie was still soundly asleep, with her toys laid out just inches away.
Post-mortem results suggested the innocent teenager managed to put up a struggle but was unable to fight off her attacker.
The court heard Edwards told detectives her sister mumbled the words: “I can’t…” in a “scary voice” which was “all croaky” as she lay dying.
“I saw him go into her (Katie’s) room with the knife and think I heard her say ‘get off me’ and ‘I can’t’ but she couldn’t say the word ‘breathe’,” she said in a police interview.
“He used his full body weight and covered her face with a pillow. When he came out he had blood on his face and hands and on his jumper.”
After the “cold, calculated and callous” killings on April 13, Edwards left a suicide note titled “f*** you world”, the court was told.
The note said: “I want to be cremated and I want mine and [Markham’s] ashes to be scattered at our special place. We don’t give a f**k any more.”
She and Markham also both took a bath together, watched Twilight and had sex.
Edwards denied murder, claiming to be suffering from an abnormality of mental function which impaired her ability to form rational judgments.
However, police said she and her boyfriend had planned the killings for a “while” and were in “full agreement”.
The pair hatched the plot in a McDonald’s restaurant before plotting the night of April 13 to chilling precision.
Det Con Dawn Watts said Edwards, who claimed her mum favoured her sister, told of how her plan to kill them started as “a joke” that “escalated”.
A jury heard that in a police interview, the teenager claimed she “felt like murdering for quite a while”. She also said knives were “the best solution” because they could not get hold of a gun, the court was told.
Edwards is said to have told officers she had “been a disaster from day one” and felt like “an emotional train wreck”.
Just 10 days before she helped to murder her mother, the pair had exchanged light-hearted messages on Facebook.
The conversation on the night of April 3 began after Elizabeth spotted that her daughter had posted a new profile picture of herself.
In the image, the teenager could be seen looking directly at the camera lens, unsmiling and wearing black-framed glasses.
A few hours after the image first appeared, her mother said to her: “Where’s your beautiful smile? x” A minute later, her daughter replied: “It disappeared x.”
Her mother asked: “Why hun? x”, with Edwards replying: “I don’t know x”, with a series of emojis including a smiley face trailing after her comment.
Mrs Edwards then commented “I think it’s under ur bed lol x,” posted along with cartoon images of cute and cuddly cartoon animals pictured sleeping.
Edwards was found by police lying under a duvet in front of the TV with Markham after murdering her mum and sister, whose bodies lay upstairs.
In the weeks after her arrest, she showed no trace of remorse for her crimes.
She later told a psychiatrist she was “a bit sad” about her sibling’s fate but “glad” her mother was dead, the court was told.
In October 2015, Lincolnshire Police had put out an appeal after Edwards and Markham had disappeared together with just a tent.
They were missing for around three days after being seen leaving school. They took food, clothes and bicycles with them.
After being jailed for life last year, the couple launched a challenge at the Court of Appeal against their “manifestly excessive” minimum terms.
(Originally Published at mirror.co.uk, click here for more)