Wilfred Bull, 62, won a ruling from the Court of Appeal that the collection of antique horns - which was acquired legitimately - should never have been confiscated when he was convicted of trying to sell it in a conspiracy run from his prison cell.
Bull had expected the 128 horns - one of the largest collections of its type in the world - to raise about pounds 2.8m in a world market dominated by oriental buyers who sell powdered rhino horn as an aphrodisiac.
At the time that he launched his abortive attempt to sell the horns - with the help of his friends and contacts - the international trade in rhino horn was banned except for dealers with special exemption certificates.
But the strict rules laid down by the 1985 Control of Trade in Endangered Species Act were eased last year, allowing dealings in white rhino horn from South Africa.
This means that Bull, who hopes to be freed from his murder sentence after his next parole hearing in August, can now lawfully auction off at least 30 per cent of his collection - and look forward to a comfortable life with his girlfriend, Carol Scotchford-Hughes, 50.
In their ruling yesterday, three appeal judges held that Bull should not have been ordered to forfeit the horns, which were all over 30 years old and had been collected legitimately before the 1985 Act came into force.