After the press spent eight months pushing for their identities to be revealed, restrictions on naming the pair were lifted by three judges at London's Court of Appeal today and the full, harrowing facts of the case can now finally be reported.
Appeal judges also reduced their sentences to life with a shorter minimum tariff behind bars of 17-and-a-half years.
The identities of the victims could also not be disclosed during last year's trial at Nottingham Crown Court because it would have identified the defendants.
Nor could the real motive for the killings be reported: jealousy and sibling rivalry.
Kim Edwards claimed her mother loved her sister more and treated her "like an angel". She said her sister "got all the fuss" and "took my mother away from me".
The schoolgirl also held a "grudge" against her mother for hitting her in the face at a caravan park when she was just eight years old.
A police report said the Christian dinner lady "completely lost it" and hit her in the jaw in front of her sister when she complained about a television being broken.
Both girls were taken into care and spent four months with a foster family before returning to their mother. But Kim 'never forgave' her for the attack and became a "ticking time bomb".
She plotted the murders after her mother told her she was going to end up like her estranged father, Peter Edwards, who was described in court as an "abusive drug addict".
It was said he forced his wife to flee to a women's refuge and she prevented him from seeing the children as a result.
As she was growing up, Kim sought a relationship with her father and resented not being allowed to see him, because she believed "I would have been his favourite".
Churchgoing Ms Edwards strongly disapproved of her daughter's "toxic relationship" with Markham and warned her: "He's just like your dad".
Kim confided in Lucas and the pair adopted a "Bonnie and Clyde" mentality of "us against the world" - which led them to commit one of the most notorious offences in UK criminal history.
After the killings, Kim said she "got rid of the biggest problem that made me feel depressed".
In a shocking police interview, she told detectives: "Ever since I was young I never got on with my mum. I knew she favoured my sister more than me. She said she didn't but I knew she was lying.
"They would talk together and whenever I got into an argument with my mum, Katie would always take her side.
"Whenever I tried to talk to Katie she would say 'shut up' and walk away, but she always expected me to listen to her problems.
"Lucas just hates me being upset. He didn't like my mum or my sister for that reason.
"I got rid of the biggest problem that made me feel depressed, which was my mum.
"It was a relief. My mum doesn't have to deal with me being suicidal anymore and my sister doesn't have to go through the heartbreak."
Pair fought lengthy legal battle to retain their anonymity
Lucas pleaded guilty to the murders, and Kim was found guilty after a trial last year - but legal orders meant they could not be named because of their age.
Now both aged 15, they fought a behind the scenes legal battle to retain their anonymity and appeal against their sentences.
However, yesterday the Court of Appeal ruled that it was "overwhelmingly in the public interest" for them to be named.
Judge Sir Brian Leveson described it as an "exceptional case", saying the teenage killers had "jointly decided" to kill Ms Edwards and her "entirely innocent" sister.
He said the facts of the case "cannot be properly understood without identifying that the appellants murdered the mother and 13-year-old sister of Kim Edwards".
Saying there was no evidence that reporting their identities would adversely affect their future rehabilitation, he added: "The reality is that anonymity lasts only until 18 years of age and both appellants face a very considerable term of detention that will stretch long into their adult life.
"The process of reflecting on their dreadful crimes, addressing their offending behaviour and starting a process of rehabilitation will be a lengthy one."
Appeal judges also reduced Kim and Lucas's sentences to life with a shorter minimum tarrif behind bars of 17-and-a-half years.
When sentencing the pair Mr Justice Haddon-Cave said the case had "few parallels in modern criminal history".
He said they had a 'toxic' relationship, and acted in a grotesque way after the stabbings.
Mr Justice Haddon-Cave told the teenagers: "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."
How the couple met
The court heard Kim first became aware of Lucas in September 2013 when he threw a chair across the room in an English class.
They began hanging out in January the next year and discovered they had the same attitude to life, saying "it was s*** and it was going down hill".
Lucas asked Kim out on Facebook on May 23, 2015 after discovering she fancied him, and the pair embarked on their "intense, toxic relationship".
Lucas was excluded from Gleed Academy in Spalding where the two were at school and moved to First Steps School in Boston, Lincolnshire, in March.
Outside school, the couple isolated themselves from everyone and retreated into their own increasingly dark world, writing about self-harm, suicide and depression on the internet which eventually culminated in their murderous plan.
Bloodbath was planned in brutal, meticulous detail over days, possibly weeks
Kim said she had felt like murdering 'for quite a while' but it was on April 11, 2016 the murder plot was hatched in her own back garden.
Lucas "jokingly" told his girlfriend: "I really want to kill your mum." She replied: "So do I" and the plot escalated - with Edwards as the "driver".
They decided he would murder Ms Edwards and she would kill her sister to save her the agony of finding their mother's body.
The sweethearts agreed to each take an overdose of tablets with alcohol after the killings so police would find all four of their bodies inside the house.
Kim told detectives there were two botched murder attempts on consecutive nights when she had arranged to let Markham in but "unfortunately fell asleep".
The couple met at a McDonald's after school on April 13 where she insisted the plan was still on and gave him the go-ahead.
At around midnight, Markham returned with a bag containing four knives he had taken from his kitchen drawer.
After scaling the Edwards' garden fence he climbed onto a shed roof and crawled towards the girls' bedroom.
He knocked the window three times and she let him in through the bathroom window.
In a chilling account of her "cold, calculated killing" Kim said he climbed through and handed her his backpack containing six kitchen knives.
She said: "I unzipped the bag and Lucas said: 'Are you sure you want to do this?' I said yes but I said I didn't exactly want to kill my sister. He said: 'Ok, I will do it instead.'
"He got one of the large knives and he went into mum's room."
He crept into Ms Edwards' room first, knelt over her on the bed and plunged the eight-inch blade into her neck repeatedly during a 10 minute frenzied attack before smothering her with a pillow.
Kim rushed in when she heard her mother "kick out and gurgling" because she wanted to make sure Lucas was not hurt.
In the commotion she saw her boyfriend's hand, reached out and held it - "but then I realised it wasn't Lucas's", she said.
She described how "my mum's hand was cold. It was while her nerves were still reacting."
Lucas clinically checked Ms Edwards' pulse to make sure she was dead.
Kim later remarked that "a gun would have been easier".
Lucas then sneaked into Katie's room where he stabbed and smothered the young girl to death.
Kim returned to the bathroom because she "didn't want to watch again". She heard her sister's final words: "Get off me... I can't..."
Killers showed "no remorse" after the murders
Kim then ran a bath because she "doesn't like the smell of blood" and they washed together for 20 minutes.
She then got dressed into pyjamas patterned with yellow minion characters from the movie Despicable Me, covered Katie with a blanket and dragged Kim's mattress downstairs.
The couple then "got the drink in", had sex and watched three of Twilight films while eating "ice cream and toasted tea cakes" in the early hours of April 14.
Kim and Lucas had planned to commit suicide at 2pm, but Kim said "for some reason it never happened" and they watched the fourth episode of Twilight instead.
A suicide note was found that read: "I want Lucas and my ashes scattered at our special place. From Lucas and Kim, we don't give a f*** anymore."
On the morning of April 15, police officers burst into the house and asked where Elizabeth and Katie Edwards were, to which Kim responded: "Upstairs".
When asked what had happened to them Lucas chillingly replied: "Why don't you go and see?"
Throughout the trial Kim was accused of showing "no hint of remorse" and - although she did not commit the actual stabbings - of being "the driver" behind the couple.
After the bloodbath she described how she and her boyfriend "felt fine" - and said that she had "felt like murdering for quite a while".
Emphasising the apathy Kim showed towards her mother and sister, prosecutor Mr Peter Joyce QC said: "Afterwards she said she felt 'a bit sad".
"A bit sad" - as if it was a goldfish or a hamster'.
After the ruling, Detective Superintendent Martin Holvey, head of Major Crime at Lincolnshire Police, said: "The judges have ruled that there is a strong public interest in the full facts of this exceptional case being known, meaning that Lucas Markham and Kim Edwards can now be named.
"The murders of Elizabeth and Katie Edwards were horrific and brutal and the whole country shared a sense of shock that two juveniles, who were only 14 years old at the time, could have carried out such a horrendous act.
"I'm sure that sense of disbelief and horror will be deepened now it is known that it was Elizabeth's own daughter who was responsible for plotting with her boyfriend to carry out the murders.
"Evidence heard in court that was previously restricted can now be reported..
"These include details about the behaviour and actions of Kim Edwards and Lucas Markham afterwards, which was chilling.
"They remained downstairs in the house, watching TV and eating food, whilst the bodies were upstairs.
"They showed no remorse at all when they were eventually found by officers and during their police interviews.
"These new revelations about the case will undoubtedly focus attention on Spalding once again and I would like to repeat sentiments I have made earlier, thanking the community for their cooperation throughout the case and paying tribute to the courage of Elizabeth and Katie's family.
"They have endured a terrible ordeal and faced the additional anguish of knowing that this horrific crime was committed by a family member".
