IANAL, but in the US, I think only government agencies are barred from introducing illegally-obtained evidence.

I could be wrong, but I think that if I (as a private citizen, not affiliated with any law enforcement agency) steal evidence to submit to the police, then that evidence is still admissible in court, provided no government agent solicited me to steal it. However, I would still be guilty of any crimes I committed to obtain that evidence.

Sort of like how Facebook isn't subject to the first amendment. The bill of rights only protects against government actions.