Why not move Marius?
The Copenhagen Zoo had turned down offers from at least two other zoos to take Marius and an offer from a private individual who wanted to buy the giraffe for 500,000 euros ($680,000).
A spokesman for the institute, Tobias Stenbaek Bro, told AP that a significant part of EAZA membership is that the zoos don't own the animals themselves, but govern them, and therefore can't sell them to anyone outside the organisation that doesn't follow the same set of rules.
He said the zoo had followed the recommendation of the EAZA to put down Marius because there were already a lot of giraffes with similar genes in the organisation's breeding programme.
Bengt Holst, Copenhagen Zoo's scientific director, said it had turned down an offer from Yorkshire Wildlife Park in the UK, which is a member of EAZA, because Marius' older brother lives there and the park's space could be better used by a "genetically more valuable giraffe".
EAZA said it supported the zoo's decision to "humanely put the animal down and believes strongly in the need for genetic and demographic management within animals in human care".