Accomplice liability is the legal theory used to charge people with aiding and abetting. The accomplice can be charged as a principle even through they didn't physically commit the crime. So if you aid the Hamburglar, you can also be charged with hamburglary.

Accomplice liability usually requires a purposefully mens rea, although some jurisdictions use knowingly for serious crimes like rape and murder. You cannot recklessly/negligently aid and abet.

Hicks v. United States (1893)

Facts
Hicks and Culvert were sitting on horses when Row walked up. Row raised his rifle twice and each time pointed it at Culvert. Hicks said, "Take off your hat and die like a man." Hicks was also taking off his own hat and laughing. Row shot and killed Culvert. Hicks and Row rode off together.

Hicks was indicted for murder under accomplice liability. A jury instruction expressed that Hicks was guilty if his actions encouraged Row to shoot Culvert. Hicks argued that he feared for his own life, and was only trying to diffuse the situation with humor.

Question
Was this jury instruction correct?

Holding
No

Reasoning
The instruction should have added that the defendant had to intend to encourage the killing.

And the winner is...
The case was sent back for retrial.

State v. Gladstone (1980, Washington)

Facts
An undercover agent was trying to buy pot from Gladstone. Gladstone wasn't holding, but he drew the agent a map to another dealer. The agent went and bought pot. Gladstone was charged with aiding and abetting the other dealer in selling drugs.

Question
Was there intent to sell drugs?

Holding
No

Reasoning
Gladstone was knowing, but not purposeful. The state did not produce evidence that Gladstone cared whether there was a drug deal. His alleged ambivalence set him free. Plus, that's just good customer service.

People v. Luparello (1987, California)

Facts
Luparello was jealous because his former lover married someone else. He thought he could locate the couple through an acquaintance named Martin. Luparello convinced his friends to go beat the information out of Martin. They showed up at Martin's residence with guns and a sword (in 1987!), lured him outside, and ultimately shot and killed him.

Luparello was charged with aiding and abetting murder. He argued that the murder was unplanned, unintended, and unrequested.

Question
Is Luparello liable for murder?

Holding
Yes

Reasoning
California used a "natural and foreseeable consequences" test. Death was a natural and foreseeable consequence of Luparello's request.

Notes
This is a minority view. As in the previous two cases, the MPC would not honor this principle because it establishes only negligence and at most recklessness. I mostly just included this case because of the ridiculous sword-wielding business.

summarized from Life of a Law Student