In the June 15, 1969 issue of The Libertarian Forum, in an article “Massacre at People’s Park,” Murray Rothbard writes:
The cry has gone up that all this was necessary to defend the “private property” of the University of California. In the first place, even if this little lot was private property, the bayoneting, gassing, torturing, and shooting of these unarmed park-developers would have been “overkill” so excessive and grotesque as to be mass murder and torture and therefore far more criminal than the original trespass on the lot. You do not machine-run [sic] someone for stealing an apple; this is punishment so far beyond the proportion that “fits the crime” as to be itself far more criminal than the original infraction. So that even if this property were legitimately private the massacre is still to be condemned.
Secondly, it is surely grotesquerie to call the muddy lot “private property”. The University of California is a governmental institution which acquires its funds and its property from mulcting the taxpayers. It is not in any sense private property then, but stolen property, and as such is morally unowned, and subject to the libertarian homesteading principle which we discuss below. The people of Berkeley were homesteaders in the best American—and libertarian—tradition, taking an unused, morally unowned, muddy lot, and transforming it by their homesteading labor into a pleasant and useful people’s park. For this they were massacred.
This has hints of the leftist and left-libertarian view of property rights—that if there is “taint” or “original sin” in the origin of title to current possessed resources, then the title is not legitimate, and the resource may be regarded as “unowned” and is legitimately subject to homesteading. Why something that is stolen is to be regarded as unowned, as opposed to owned by some dispossessed claimants and original owners, is not clear, and seems to contradict later writing by Rothbard.
But in any case, later writing by Rothbard, as of 1974 at the latest, seems to reject any such implications. As I noted in my post Justice and Property Rights: Rothbard on Scarcity, Property, Contracts…, Rothbard published his article “Justice and Property Rights,” 1974, and in two forms: first, in Egalitarianism as a Revolt Against Nature and Other Essays, which is available online here; and also, a second version, in Property in a Humane Economy, Samuel L. Blumenfeld, ed. (one of these versions, I can’t remember which, was included in The Logic Action One, which is not online). The two pieces seem identical but the latter version, from the Blumenthal collection, appends an important concluding paragraph that is not present in the earlier version:
It might be charged that our theory of justice in property titles is deficient because in the real world most landed (and even other) property has a past history so tangled that it becomes impossible to identify who or what has committed coercion and therefore who the current just owner may be. But the point of the “homestead principle” is that if we don’t know what crimes have been committed in acquiring the property in the past, or if we don’t know the victims or their heirs, then the current owner becomes the legitimate and just owner on homestead grounds. In short, if Jones owns a piece of land at the present time, and we don’t know what crimes were committed to arrive at the current title, then Jones, as the current owner, becomes as fully legitimate a property owner of this land as he does over his own person. Overthrow of existing property title only becomes legitimate if the victims or their heirs can present an authenticated, demonstrable, and specific claim to the property. Failing such conditions, existing landowners possess a fully moral right to their property.
It appears that language was added by Rothbard to combat the arguments of some, such as some left-libertarians, who want to argue that existing property titles are illegitimate because of their non-immaculate origins and, presumably, ought to be wrested from current nominal owners, especially the wealthy, and I suppose redistributed to the proles.
Or, as Rothbard wrote in ch. 9 of The Ethics of Liberty (1982):
To sum up, for any property currently claimed and used: (a) if we know clearly that there was no criminal origin to its current title, then obviously the current title is legitimate, just and valid; (b) if wedon’t know whether the current title had any criminal origins, but can’t find out either way, then the hypothetically “unowned” property reverts instantaneously and justly to its current possessor; (c) if wedo know that the title is originally criminal, but can’t find the victim or his heirs, then (cl) if the current title-holder was not the criminal aggressor against the property, then it reverts to him justly as the first owner of a hypothetically unowned property. But (c2) if the current titleholder is himself the criminal or one of the criminals who stole the property, then clearly he is properly to be deprived of it, and it then reverts to the first man who takes it out of its unowned state and appropriates it for his use. And finally, (d) if the current title is the result of crime, and the victim or his heirs can be found, then the title properly reverts immediately to the latter, without compensation to the criminal or to the other holders of the unjust title.
I do not see a closely corresponding passage in For A New Liberty (1973) (I stand to be corrected on this), so it appears to me that sometime between 1969 and 1973, Rothbard’s thought on this matter developed.
See also the related thoughts of thinkers like Mises and Hoppe on this issue, as discussed in Mises, Rothbard, and Hoppe on the “Original Sin” in the Distribution of Property Rights.