Why? Well this is the disgusting bit; The judiciary has ruled that time is up for pre-trial custody. These people have over 800 cases to answer for, but not one of them has been moved forward sufficiently by Argentina's congress to make it to trial as yet. So the judiciary blames congress, and congress blames judiciary and the flotsam and jetsam of this world get out of jail. In the case of the most famous of the lot, Alfredo Astiz, he's been in jail since 2003 but not one case has been brought against him yet. This is worse than ridiculous. To give you an idea of the calibre of the man Astiz in a context that gringos might understand better, British war veterans of the Falklands/Malvinas conflict remember him as the guy who ordered his troops to fly white flags at Goose Green then, when the British soldiers got close enough, ordered the same soldiers to open fire. As for his exploits during the disappearances, as well as being one of the head torturers at ESMA he was the guy who condemned two French nuns to death during his undercover work, the signal for those watching being a kiss on the cheek of the nuns. Crud like Astiz, "El Tigre" Acosta and all the others should rot in jail forever, but because of the laxity and collusion from passive friends-in-high-places he'll now walk free.
UPDATE: I should have checked first. Lillie at Memory in Latin America is all over this story and does a far better job of telling it, too. Here's the link, Go see.