Two 15-year-olds have been detained for killing a man in south London to "teach him a lesson" after one of them accused of him of sex abuse.
Robert Daley, 45, was stabbed at his Brixton flat, hours after another abuse case against him was dropped in April.
Last month the boy was convicted of murder and the girl of manslaughter.
The boy was given a life term with a minimum of nine years. The girl, who said Mr Daley had indecently touched her, was sentenced to six years.
The teenagers, who cannot be named as they are underage, were both 14 at the time of the stabbing.
Jurors heard the girl, her older sister, then aged 15, and a woman had complained to police that Mr Daley had abused them.
He was attacked hours after the Crown Prosecution Service (CPS) called to tell him it was dropping a case involving an allegation of sexual assault against him due to insufficient evidence.
Soon after the call from the CPS, Mr Daley called the older girl and "gloated" about the case being dropped.
The upset girl texted him back calling him a "perverted man", the court heard.
The girl, who is now 16, then called her boyfriend and her younger sister who went to Mr Daley's flat in Fosbury House, Brixton.
The boy - who had been excluded from school four times for knife possession and threatening a pupil - is thought to have been involved with gangs.
'Acting in revenge'
He told the jury he stabbed Mr Daley to save the 15-year-old girl, as she was being choked by the victim.
But Judge Anthony Morris told the boy: "You saw what you were doing as acting in revenge for what you saw as an insult to your girlfriend."
Following the killing, the pair disposed of the knife, a mobile phone and bloodstained clothing before splitting up and meeting later at a friend's house.
"You both showed chilling criminal sophistication for 14-year-olds," the judge added.
The female was described as "an intelligent girl who has poor control over her temper and a tendency to be aggressive to others".
She had also been excluded from school for "extreme verbal abuse" to members of staff.
Since the killing she has been involved in eight incidents including five assaults.
The victim, who had a severe drink problem and took drugs, was stabbed five times.
The judge said he was prepared to accept that the allegations against Mr Daley were true but he added it was "understandable" for the CPS in the particular circumstances not to proceed.
Jonathan Rees QC, prosecuting, told jurors Mr Daley may have been a "Jekyll and Hyde character" but added: "This is not a vigilante society."
He continued: "The question you have to deal with is not whether he deserved what he got but whether he was murdered.
"We maintain that the defendants set out to teach him a lesson."