The case of  Thompson v. US 155 U.S. 271 (1894)

The case of Thompson v. US stands for the principle merely carrying a firearm is not evidence of murder or manslaughter.  Instead the court expects people to arm themselves when threatened.   In this case Thompson, a Creek Indian boy, was threatened by Mr. Hermes because Mr. Hermes thought that Thompson harmed a pig.  Thompson returned home by a road that went through the same area that the threat occurred in and Mr. Hermes lived in. 

Thompson armed himself with a Winchester rifle and was returning home.  However the trip home was through the same area Mr Hermes lived in and was the only reasonable route home.  The deceased made the final and fatal mistake of threatening Thompson and going for a gun against a Winchester. 

This case was ruled upon the issues of: Intent and retreat

Similar cases on Intent were Gourko, Allen and Wallace on intent and Beard, Rowe, Alberty and Brown on Retreat.  Notice that in this case the only reasonable route home was by or through the aggressors property. The Court ruled that there was no duty to retreat or avoid going home even though the danger was known and then ruled that arming himself due to the prior threat was reasonable and not Murder. 

On the issue of intent.  It is normal reasonable and expectable for a person to arm themselves when placed in danger.  The court in this cases  focuses on whether the use of deadly force and self defense was proper and totally rejects the proposition that arming ones self is of itself is evil or any evidence of wrong doing.  The court assumes and expects that people own and bear weapons especially if threatened or at risk.  Owning a gun is normal behavior and legitimate behavior in a peace loving society.  To imply that this lawful activity was evidence of manslaughter or murder was judicial error per se.  In reversing this case the court sarcastically uses the term "learned" and then cites each error in criticizing the judge as an idiot.  This is one of several cases like Gourko where the Court punished Hanging Judge Parker and criticized him for his dislike of self defense.  Judge Parkers strong dislike of guns championed the response from the Supreme Court to establish the right of self defense and the individual to bear arms. 

Every situation is different however and this is for information only.  This is not legal advice.