Mario Celaire was told he faces a "very significant" jail term
A footballer who was found not guilty of murdering his ex-girlfriend has admitted killing her after new evidence from a second victim came to light.
Mario Celaire, 31, from Sydenham, south-east London, was cleared in 2002 of killing Cassandra McDermott, 19.
He was prosecuted again under "double jeopardy" laws after his next victim Kara Hoyte, 19, told police Celaire confessed to killing Miss McDermott.
Celaire admitted manslaughter and attempted murder at the Old Bailey.
The court heard that Celaire, a former Maidstone United player, had a history of physically abusing Miss McDermott.
He began stalking her after she ended their four-year relationship and met a new man.
Miss McDermott was killed while house-sitting at her mother's home in Norbury, south London, in October 2001.
The court heard that Celaire either punched Miss McDermott or pushed her head into furniture, knocking her out and leaving her to choke to death.
Celaire physically abused Cassandra McDermott during their relationship
Celaire, who also called himself Mario McNish, was cleared of killing Miss McDermott by a jury in 2002.
His relationship with Miss Hoyte followed a similar pattern and he attacked her with a hammer after they split in February 2007.
Miss Hoyte was left with brain damage and partial paralysis, and was barely able to communicate.
However nine months after Celaire attacked her, Miss Hoyte told police that he had admitted killing Miss McDermott after Miss Hoyte found case papers from his trial and challenged him about it.
Since Celaire's original trial, the has law been changed to enable someone to be prosecuted more than once for serious offences such as murder where "compelling new evidence" exists - a process known as "double jeopardy".
Prosecuting, Simon Denison QC said the new investigation into Miss McDermott's death found fresh evidence of Celaire's previous violence towards her and others.
On Thursday Celaire admitted the manslaughter of Miss McDermott and the attempted murder of Miss Hoyte. The 2002 jury verdict was quashed.
Scotland Yard said it was the first Metropolitan Police prosecution under "double jeopardy" since the law changed in 2003.
Judge Paul Worsley warned Celaire that he faced a "very significant" jail term when he is sentenced on 3 July.
Outside court Miss McDermott's sister Andrea said: "We knew Mario killed Cassie. Today we have been vindicated.
"We have had to wait eight years for it - eight years of hell."
Miss McDermott's mother Jennifer said: "It is a victory for everyone who feels that they have been let down by the justice system.
"This double jeopardy will give people the chance to say 'we can go back and fight again, we won't give up'."