The facts were: (in the case I'm thinking of)
Two people attacked one other, there was bad blood between them and anecdotal evidence exists to suggest they went out looking for the victim. During the attack he was beaten to the ground and then
both attackers
repeatedly jumped up and down on his head.
In that case I'd say both should have been found guilty of murder.
Both pled guilty to culpable homicide (equivalent to manslaughter in Scots law) and got sentences of about 9 years each, with the usual reductions for time on remand and automatic 1/2 way release. The pleas were accepted as they were arguing they didn't mean to kill the victim, the jumping on the head just got out of hand...
I suppose given Scotland has a 'Not Proven' verdict it may be slightly different but in my book both should be on a life sentence right now.