Her distraught father, Paul, broke the news at a press conference at which he renewed appeals for action against drug dealers and said he took comfort from Leah's organs being used for transplant.
Leah, of Latchingdon near Maldon, Essex, had been in a coma at Broomfield Hospital, Chelmsford, since collapsing just after midnight on Sunday after taking one ecstasy tablet at her 18th birthday party.
After four days in which the teenager showed no signs of improvement, the decision to switch off the life-support was made on Wednesday evening and carried out early yesterday. Just a few hours later, Mr Betts and his wife, Janet, faced the press and wept as he said: "Leah's ordeal is now over."
In an emotional outpouring, Mr Betts, a former officer in the Metropolitan Police, called for a radical review of the sentencing of drug dealers and spoke of his hatred for those he accused of killing his daughter.
"The hatred I have got is welling up inside me not only as a father but as an ex-policeman. I think there has to be a complete radical change in the way people are dealt with," he said.
Drug dealers should serve the sentence passed "instead of being sentenced to five years and then you let them out after five months".
"That is the biggest load of bull I have come across. What deterrent is that? It killed my daughter and it is killing others."
Mr Betts said he would treasure memories of his daughter "from bouncing her on my knee to when she came running down the hall on Saturday night dressed in her new outfit, saying 'how do I look?' She looked so beautiful".
His wife, Leah's stepmother, who is a nurse, repeated a warning to those who take drugs. "I could lecture like a mum until I am blue in the face, but the only people who can prevent this from happening again is yourself."
She said she was horrified by people "sitting around discussing the virtues of these drugs" and by the notion of testing tablets to check the purity. She stressed that the ecstasy which claimed Leah's life was the straight, unadulterated chemical compound.
Mrs Betts added: "To people who say it's her own fault, you are right, but drugs should not be available in the first place and peer pressure should be to refuse them and not take them. This fashion must die like our daughter has died."
Mr and Mrs Betts, together with Leah's three sisters and a brother, had kept a vigil at her bedside. They thanked the intensive care unit staff, the transplant teams and the public who have inundated the family with letters and cards of support. Some came from children who had stopped taking drugs after seeing what had happened.
Mr Betts said: "If there are any others I can help - by talking to groups, families, anything whatever having lived this living hell I would be only too willing to assist in any way I can."
Last night a young woman was recovering at Papworth Hospital, Cambridge, after being given Leah's heart at 6am yesterday morning, about four hours after the teenager died.
Vanessa Morgan, transplant co-ordinator for Essex and north London, met Leah's parents on Wednesday after they told intensive care staff they wished their daughter's organs to be donated. She said: "A young death like this is such a tragedy that getting something positive out of it must be good."
Leah is thought to have bought the tablet at a night club in Basildon last Friday. Police yesterday repeated appeals for with information.
Last night police made their 13th arrest in connection with the inquiry.Reuse content