Mark Hughes: Jail again for the addict who 'enjoyed gratuitous violence'

In the witness box at the Old Bailey, Dano Sonnex told the jury of a memory from his childhood. It was of a police raid on his house in which officers had, he said, beaten his father almost to death as they searched his family home in vain for guns and drugs.

The telling of the anecdote was used as an attempt to explain his lack of faith in the authorities: "I don't trust the police at all," he said. Instead it gave a telling insight into his family's life of crime, showing that even his earliest recollections were of police involvement with members of his lawless family.

Before yesterday's verdicts, the prosecution told the court that the Sonnex family, from Deptford in south-east London, had 83 separate criminal offences to their names. With Dano's convictions yesterday – two counts of murder, two of false imprisonment, burglary and arson – that total now stands at 89.

Bernard Sonnex senior, Dano's father, has appeared in court 26 times, charged with 47 offences including gun and drug offences, the jury was told. The 56-year-old has been to prison six times. Bernie junior, Dano's older brother, has had 21 court appearances and has been charged with 34 offences. The 36-year-old has had 10 separate spells at Her Majesty's pleasure.

While Bernard senior appeared in the public gallery at the start of last month's trial, Bernie junior could not be there to support his brother. He was in prison. That sentence was imposed for an offence that took place from behind bars when he threatened a witness who was due to testify against him in a robbery trial. He told the woman: "You do not want to go to court", and said he was "the master of control". He was released last month, just days before the trial concluded.

Nigel Farmer told the court that Bernie once shot a pub DJ five times in the head with a gas gun when the man refused to play a Bob Marley song but "nobody in the pub had given evidence against Bernie because they were scared". According to Farmer, Bernie junior also bragged that he had killed three people and had "got away with every single one of them".

Their sister Louise, 35, is also a criminal. She is in Holloway prison after being sentenced to five years in March for causing grevious bodily harm with intent. The victim was her father's girlfriend, whom she had followed on a bus and then attacked with a golf club. She has a previous conviction for wounding with intent when she glassed another woman in a pub.

And then there is Daniel "Dano" Sonnex. A habitual drug user, he has spent only four months of his adult life out of prison. His first brush with the law was in December 2001 when he was cautioned for possession of cannabis. His first chargeable offence was in May 2002 when, aged 16, he stabbed another teenager three times after an argument over a car.

Then, in September 2002, he and another man robbed four young people of their bags and wallets with an imitation firearm. During one of the robberies he held a gun to the head of a young girl and laughed, saying: "This is how we fuckin' do it."

He was caught and pleaded guilty to wounding with intent and robbery. He was sentenced, in March 2003, to eight years in prison. During his time behind bars he was reprimanded 41 times for incidents of violence and taking drugs and once for setting fire to his cell.

He was refused parole twice, but in February 2008 he was released on licence at the mandatory two-thirds point of his sentence. Two days after his release he was alleged to have been involved in an incident which bore chilling similarities to the ordeal he would later put Laurent Bonomo and Gabriel Ferez through.

With an accomplice, he allegedly tied up a pregnant relative and her boyfriend, using cable ties to bind them at the ankles and wrists. After pillow cases were placed over their heads, Sonnex was said to have threatened them with a hammer and a saw and demanded money. The pair escaped and called the police, but later withdrew their complaints. Sonnex was never charged.

As well as dealing drugs, Sonnex admitted he had carried out more than 10 burglaries in the two weeks before the murders. It was also revealed that he tried to burgle the house of the Eastenders actress Maureen Bass, who plays "Big Mo" in the soap, an hour before the killing.

As well as his constant criminal pursuits, Sonnex's temper and aggression gave cause for concern. He has never been diagnosed with a mental illness, but his brother's girlfriend, Fay Culyer, described him as "not right in the head" and prosecutors said he was someone who "enjoys using gratuitous violence".

Sonnex himself appears to have recognised that he was a danger to society. In 2004, while in Portland Young Offenders' Institution, he told a prison doctor that he was worried his reactions to things that angered him meant that he "could kill".

His reaction after being arrested for the murders was to tell a police officer: "I'm going to bite your face off." While in the back of the police van Sonnex "laughed hysterically" on his way to the station. The officer who arrested him said his behaviour was "very odd, bearing in mind what he'd been arrested for."

While not as criminally prolific as the Sonnex clan, Dublin-born Nigel Farmer does have a previous conviction for knifepoint robbery. He says his life hit an "all-time low" in October 2007 when he split up with his partner of 10 years and was no longer allowed to see his twin sons.

The 34-year-old's recreational drug habit intensified to the point where he was spending £60 a day on crack cocaine and £40 a day on heroin. He twice tried to kill himself by slashing his wrists and in May 2008 he checked into a psychiatric hospital. But he discharged himself after four days saying that the treatment he was receiving was "not the right sort of help at all".

He then moved in with the Sonnex family. During the trial the pair blamed each other. Sonnex, who continually changed his evidence, claimed they had been robbed at a club earlier in the night and that the robbery in Sterling Gardens – Mr Bonomo's flat – was Farmer's idea as a way of recouping what they had lost.

Farmer denied being present but admitted later starting a fire at the flat to try to cover up evidence, saying he did it because he was scared of the Sonnex brothers. He said Dano had told him that if he did not set the fire he would cut off his children's legs. But the jury, by a majority 11-1, dismissed their implausible story and, after five days of deliberation, convicted them. As they were led from the Old Bailey's court number one, the pair looked at each other. Accepting his lies had failed, Sonnex simply shrugged his shoulders.