Mr Lamb was beaten up and stabbed with a knife and a pitchfork in an Edinburgh street.
A court heard how one of the accused, James Watson, was released from a five year sentence just a week before he took Mr Lamb’s life.
On the night of the murder Watson, his brother Paul and friend Gary Sim went to the Tor pub in Restalrig Road to celebrate Watson’s release.
Once there, Sim assaulted Mr Lamb and later in the evening he and his callous pals confronted Mr Lamb again in the street at Restalrig Circus.
Stunned residents heard the men shouting during the horrific attack. One witness told the high court that she heard one of the attackers say “will I finish him off?”
At the same time, the court heard how the three men had kicked and jumped on Mr Lamb’s head before repeatedly striking him on the body with a garden fork and knife.
Their victim had recently celebrated his birthday and prosecutors haven’t been able to establish a motive for the crime.
On Friday, a jury convicted the three men of murder.
Judge Lord McEwan sentenced the trio to life imprisonment and ordered the three thugs to each serve a minimum of 20 years in custody.
Passing sentence, the judge added: “This was a wanton, despicable and disgraceful attack in the streets of Edinburgh which was undoubtedly fuelled by alcohol.
“None of you are of good character. Sim, you have a deplorable record.
“The penalty is fixed by law to be life. As I cannot distinguish between any of you, I shall impose the punishment part of the sentence to be 20 years.”
The three men had spent the three week long trial denying that they had murdered Mr Lamb.
But prosecutors had managed to compile enough forensic and eyewitness evidence to prove their guilt.
After sentencing, Lord McEwan ordered the three men to be taken from the court to the cells of the High Court in Edinburgh to begin their life sentences.