Griffin also admitted attempted robbery before the trial and McDonnell was convicted of the same offence by the jury.
Judge Kristina Montgomery KC said the victim was “active and independent” and the two men’s actions caused his family “profound grief”.
She said McDonnell did not play a minor role and the case was “joint enterprise in the truest sense”.
While the court heard McDonnell was sorry to the victim’s family for what happened, the judge said Griffin never showed any true accountability or remorse.
“You have lied and lied in the course of the investigatory stages of this case and in your evidence before the jury,” she told Griffin.
The two defendants had a number of previous convictions dating back decades for offences such as burglary, robbery and weapons offences, the court heard.