The six men responsible for the murder of Mary-Ann
Indrit Krasniqi, 18, of Chiswick, west London, was convicted on Monday. Four men had already been found guilty and a fifth man had admitted the murder.
Four of the gang were on probation at the time of the killing in Reading, Berkshire, it has been revealed.
Home Secretary Charles Clarke said it was "vital" lessons were learned. Sentencing was adjourned to 28 April.
Drug-dealer Adrian Thomas, 20, of Battersea, and fellow gang-members Michael Johnson, 19, of Southfields, Jamaile Morally, 22, of Balham, and Krasniqi were all under supervision when the 16-year-old was stabbed to death and her friend shot in the head in May 2005.
I deeply regret the tragic death
- Charles Clarke
Case puts focus on probation
Thomas, Morally, Morally's brother Joshua, 23, of Balham, and their friend Llewellyn Adams, 24, also from Balham, were found guilty of the killing on Friday while Johnson, of Southfields, confessed during the eight-week trial.
They were also convicted of various charges of rape, assault, kidnap and attempted murder.
Krasniqi was also found guilty of attempted murder but cleared on two counts of rape on Monday. He had been convicted of kidnap and assault on Friday.
Speaking outside Reading Crown Court, Mary-Anne's uncle, Charles Harris, told reporters it had been a harrowing time for the family.
He said: "Very traumatic, very traumatic. Like I said, it's a big weight off our shoulders and it would be nice to put Mary-Ann to rest properly now. That's all I want to say, thank you."
Mary-Ann was found dead in a park in Reading
Home Secretary Charles Clarke said he would be studying the case with a view to making changes to the system of managing criminals on probation.
He said: "I deeply regret the tragic death of Mary-Ann Leneghan and my thoughts and sympathies go out to Mary-Ann's family and friends as well as to the other victim in this dreadful case.
"Public protection remains my absolute priority and it will continue to guide this government's policies and practices.
"It is always disturbing when a serious crime is committed by offenders under supervision in the community.
"It is vital that we learn any lessons we can from these cases and take any steps necessary to ensure that offenders are properly managed and the public are properly protected."
The trial was told that Mary-Ann and an older friend, who cannot be named for legal reasons, were abducted in the town in the early hours of 7 May last year.
The killing was a revenge execution for a robbery which Thomas believed the girls had "set up".
After a three-hour ordeal of torture and rape in a hotel room they were driven in the boot of Adams' car to nearby Prospect Park where Mary-Ann's friend was forced to watch as the younger girl was "butchered" in front of her.
As Mary-Ann lay dying, her friend had a gun put to her head and was shot at point blank range.
But she survived and went on to give evidence against her six attackers.
They all need to be put down for the better of society.