Common intention is used when charging a group of people for a crime.
It is a way to charge people , not a crime itself.
An example would be when a group of people commit theft in a dwelling, 1 person buy ladder , 1 person bring car to get away.
They all have the same intention to commit theft in a dwelling, therefore, even if they did not actually go into the house to steal things, eg, the man in the car, he can also be charged with theft in a dwelling .
Take a look a Penal Code S.34
When a criminal act is done by several persons, in furtherence of the common intention of all, each of such persons is liable for that act in the same manner as if the act were done by him alone.
P.s No Liability Accepted 
Just out of curiosity , what is the story behind this ?