Where is the line drawn between personal responsibility/influence in crimes?

[Jacobtm]

If I were to off-handedly suggest someone perpetrate a crime, and they did it, I assume I'd have no leagal responsibility for it.

However, with the case of Charles Manson, and presumably others like him, the individual in question didn't actually commit the crimes, they just convinced others to do what they wanted.

So where's the line drawn between the actual criminal taking responsibility for what they did, and someone convincing someone to do something?

[Jacobtm]

If person A asks person B to commit a crime, and actually intends that the crime be committed, then A is legally responsible. If the crime is actually committed, then person A is guilty of being an accessory to the crime; if it is not committed, then person A is guilty of solicitation.

So it just matters about person A's intent? If person A jokingly set out an elaborate plan by which to commit a crime, and person B followed that plan and actually commits teh crime, but person A was joking, is person A not responsible at all?

Could person B expect any leniency because person A convinced him to commit the crime? Would the punishment be any less for person B if they commited a crime they had thought to do themselves, versus if they had commited a crime person A had suggested/planned?