Parties
In Texas, a person can be held responsible for something that he didn't directly do. Here's the charge the jury is given when there is a question whether a person on trial was a party to the offense:
Each party to an offense may be charged with the commission of the offense. A person is criminally responsible for an offense committed by the conduct of another if, acting with intent to promote or assist the commission of the offense, he solicits, encourages, directs, aids, or attempts to aid the other person to commit the offense. Mere presence alone will not constitute one a party to an offense.
There is no distinction between accomplices and principals. Everyone who, intending that the crime be committed, helps someone else commit a crime can be convicted of the crime.
This rule can lead to extreme results - Kenneth Foster was sentenced to die based on his minimal participation as a party in a robbery that turned into a murder; his death sentence was recently commuted to life in prison - but as a principle of liability it is generally sound. Ethically as well as legally, we are responsible for the bad things that we encourage other people to do.