There are several scenarios where an individual may be charged with the criminal acts of others, even if the person was not actually present for the criminal acts and even if they did not know about all the criminal acts.
Aiding and Abetting
If one person assists another person with commission of a crime, the assisting person can be charged as a "principal" to the crime. A person who aids, promotes or encourages the commission of a crime by another person does not have to have criminal intent so long as they know about the other person's intent to commit the crime.
If one person knows that another person has committed a felony and helps the offender, the person giving assistance may be charged as an accessory to the felony.
The distinction between principals and accessories is as simple as before, during and after. If a person assists another person before or during a felony or misdemeanor, the assisting person may be charged as a principal to the felony or misdemeanor. A person may only be charged as an accessory if the crime committed by the other person was a felony crime -- there are no accessories to a misdemeanor.
Aiding and Abetting do not require an overarching agreement. Aiding and abetting are broader concepts, applying when the assisting person consciously shares in the criminal act.
If two or more people conspire to commit a crime, they are involved in a conspiracy. Conspiracy is as simple as an agreement to commit a crime and an overt act to effect the purpose of the conspiracy. The act may be taken by any party to the conspiracy.
Once a conspiracy is entered into, each conspirator is legally responsible for everything said and done in furtherance of the conspiracy by the other members of the conspiracy. In other words, once the conspiracy is in effect, a member of the conspiracy who does not "do" anything may still be charged with criminal acts by other members of the conspiracy.
Any person who commits a felony, and a death results from the commission of the felony, can be prosecuted for second degree felony murder. The felony must be dangerous to human life. When two or more people are involved in a dangerous felony and only one of them causes a death, both of them may be charged with felony murder.