Whereas I think that sin can be collaborative—some act committed by mutual agreement between two people—I also know that many crimes can be committed without anyone else being involved.
If someone robs a bank alone or kills someone in anger, these can often times be completed by a single person. Many things that are considered "sins" can be committed without the help of anyone else: such as stealing, attacking a person, threatening someone, etc.
On a purely theological note, one could argue that a collaboration exists between an inidividual and the devil. Giving in to the temptations of sin, one could say that when the person submits to the will of "the dark one" instead of resisting, sin takes place; a conscious decision is made to do something that God (and man) have governed to be wrong, and this could infer a "collaboration."