i have never heard of this before have got a link to the relvant legal precedents i would be intrested to read,
the laws of england and newyork are rather diffrent.
If you look at all the materials about UK forfeiture law you will find this over and over:
"Under the Forfeiture Rule, a person cannot benefit (e.g. inherit under a will or through intestacy) from someone whom they have unlawfully killed."
The rule when expresses always says can't benefit from someone they killed.
The 1982 Forfeiture Act actually spells out in subsection 4 what property is to be forfeited:
(4)The interests in property referred to in subsection (1) above are—
(a)any beneficial interest in property which (apart from the forfeiture rule) the offender would have acquired—
(i)under the deceased’s will (including, as respects Scotland, any writing having testamentary effect) or the law relating to intestacy or by way of ius relicti, ius relictae or legitim;
(ii)on the nomination of the deceased in accordance with the provisions of any enactment;
(iii)as a donatio mortis causa made by the deceased;
or
(iv)under a special destination (whether relating to heritable or moveable property); or .
(b)any beneficial interest in property which (apart from the forfeiture rule) the offender would have acquired in consequence of the death of the deceased, being property which, before the death, was held on trust for any person
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Note how it doesn't mention future inheritances which the deceased misses out on.
If you are asking me for any modern caselaw where a killer was prevented from inheriting from a relative other than the victims I can't find any. The original forfeiture rule awarded the state with the proceeds but that was changed in the 1880s or somewhere aroudn that time by statute.
After that the forfeiture rule was applied to prevent collecting on insurance policies taken out on the victim and in 1914 in Estate of Hall was applied to inheritance.
You might want to read Hilton v Allen (1940) 60CLR 691 because that discusses in detail the theory behind preventing one from benefiting from the victim they slay. While people assume that killers can't inherit form other estates that is not the case they simply can't inherit the estates of their victims.