It's my understanding that things left behind in a home that's been sold belong to the new homeowner.....
I'd want to see some legal authority for that. State laws might differ, but whenever I have bought or sold a home any personal property included was specifically identified in the sale documents. A failure to identify the guns as being included in the sale is strong evidence that the guns were not intended to be included and were therefore lost property.
Most States have laws dealing with lost property in general (whether a gun or anything else). Although such laws vary, the general theme is that the finder does not immediately become the lawful owner, and those laws often require that the property be turned into the police or that the finder take other reasonable steps to find the owner. For example:
- Georgia statute 16-8-6:
16-8-6. Theft of lost or mislaid property
A person commits the offense of theft of lost or mislaid property when he comes into control of property that he knows or learns to have been lost or mislaid and appropriates the property to his own use without first taking reasonable measures to restore the property to the owner.
- Kentucky KRS 514.050:
514.050 Theft of property lost, mislaid, or delivered by mistake.
(1) Except as provided in KRS 365.710, a person is guilty of theft of property lost, mislaid, or delivered by mistake when:
(a) He comes into control of the property of another that he knows to have been lost, mislaid, or delivered under a mistake as to the nature or amount of the property or the identity of the recipient; and
(b) With intent to deprive the owner thereof, he fails to take reasonable measures to restore the property to a person entitled to have it....
- California Civil Code 2080 -- 2080.1:
2080. Any person who finds a thing lost is not bound to take charge of it, unless the person is otherwise required to do so by contract or law, but when the person does take charge of it he or she is thenceforward a depositary for the owner, with the rights and obligations of a depositary for hire. ...
2080.1. (a) If the owner is unknown or has not claimed the property, the person saving or finding the property shall, if the property is of the value of one hundred dollars ($100) or more, within a reasonable time turn the property over to the police department of the city or city and county, if found therein, or to the sheriff's department of the county if found outside of city limits,...
The fact that the property is a gun can create further complications. A few States have strict rules regarding the possession of firearms. For example, in New York State one may not lawfully possess a handgun without the necessary license.
So to be sure of being on solid legal ground, the best idea would be to leave the gun where you found it, watch over it to be sure it's not disturbed, and contact local law enforcement to come and pick it up. If there was any possibility that the gun was used in a crime, law enforcement would probably want the gun left
in situ in case there might be other evidence in proximity.
...If the new homeowner decides to take possession of those firearms, is that legally the same as an in-state private transfer? Basically, would the legal principles involved be the same as if the firearms were privately transferred face-to-face by residents of the same state?....
So depending on state law regarding the finding of lost personal property, if the new homeowner just assumes ownership of the guns he might well be committing theft (or the tort of conversion).
The point is that in general the law is not, "finders-keepers." The owner of a thing isn't necessarily immediately stripped of legal title (ownership rights) to a thing if he mislays or loses it. So if you find something, you can't necessarily immediately consider it yours to keep.
I haven't done a thorough survey of the laws of all the States. I suspect that most have laws along the lines of those of Georgia, Kentucky, or California that I cited above. And in the case of a gun I think one must always consider the possibility (albeit perhaps slim) that it was "lost" on purpose because it was used in a crime.
.... Also, what if the previous homeowner had already moved out-of-state before the new homeowner moved in and took possession of the firearms? Would that count as an illegal interstate private transfer, or would the fact that the firearms were abandoned by the previous homeowner before he moved out-of-state be a factor?....
The Gun Control Act wouldn't necessarily be an issue. When the prior resident of the house lost the gun, before he moved away, he was a resident of the State in which the house is located. If the new inhabitant is moving in to make the house his home, he is becoming a resident of that State for the purposes of the GCA (unless he's only moving in during a temporary visit).
But the core issue seems to me not to be state or federal transfer laws. The core issue is that found property might not necessarily belong to the finder.
...The [California} Penal Code defines the crime of "Theft of Found Property" that would also penalize the finder, regardless of value.
Specifically PC 485:
485. One who finds lost property under circumstances which give him knowledge of or means of inquiry as to the true owner, and who appropriates such property to his own use, or to the use of another person not entitled thereto, without first making reasonable and just efforts to find the owner and to restore the property to him, is guilty of theft.