Conspiracy evidence: statements or acts by any conspirator in reference to common intention are admissible against all parties. Anything said, done or written by any one conspirator in reference to the common intention, after that intention was first entertained by any of them, is a relevant fact against each believed conspirator and may be used both to prove the existence of the conspiracy and to show that any such person was a party to it, even if they were ignorant of particular acts or the acts were done by strangers or occurred before joining or after leaving the conspiracy.