In Florida, a person can be held liable for the criminal activity of another under certain circumstances. Most recently, Florida courts have held that a parent can be charged with manslaughter if they allow their children to serve alcohol to other minors at their home. The law there is if they knew, or should have known, that minors were consuming alcohol, they are responsible for any reasonably foreseeable consequences.
Another example of principal theory can be if you are the getaway driver for a bank robbery. Even though you may never touch a gun or go into the bank, if one of your "co-conspirators" does, you can be charged with armed robbery, theft, assault or even murder if any of those crimes are committed!
Here's the law on principal theory:
If you help another person commit a crime, you are a principal and must be treated as if you had done all the things the other person or persons did if (1) you had a conscious intent that the criminal act be done and (2) you did some act or said some word which was intended to incite, cause, encourage, assist, or advise the other person or persons to actually commit the crime.
To be a principal, you don't even have to be present when the crime is committed.