"Adinolfi knows well that it is only a matter of time before a European Fukushima kills on our continent," the letter stated.
"Science in centuries past promised us a golden age, but it is pushing us towards self destruction and slavery," the group wrote, adding: "With our action we give back to you a small part of the suffering that you scientists are bringing to the world."
Adinolfi, who was discharged from hospital under police guard on Friday after he was wounded in the shooting, said "Thank God I am OK."
Before the letter arrived at the offices of Corriere della Sera in Milan, investigators had suspected the attack could be the work of the Red Brigades, the terrorist organization that kidnapped former Italian prime minister Aldo Moro in 1978.
The so-called Olga Nucleus stated that another cell within the Informal Anarchist Federation had sent a letter bomb to Italy's tax collection agency, Equitalia, in December, nearly blinding an official. Other letter bomb attacks in Italy have also been claimed by anarchist cells within the Federation.
As Italy's economy dips, Equitalia offices have become a target for violence. After an armed man briefly took hostages in an office in Bergamo last week, police on Friday clashed with protesters outside a Naples office, while a suspect package containing powder was sent to a Rome office.
On Thursday, Industry Minister Corrado Passera warned Italy's economic crisis was threatening social cohesion.
In its letter, the Olga Nucleus said it could have chosen to attack Equitalia but was not looking to win public support. "We have nothing to do with citizens who are indignant about something which doesn't work in a system in which they want to be a part," it wrote.
"We are wild lovers of freedom, and will never renounce the revolution or the complete destruction of the state and its violence."
Intellpuke: You can read this article by Guardian correspondent Tom Kington, reporting from Rome, Italy, in context here: www.guardian.co.uk/world/2012/may/11/italian-anarchists-kneecap-nuclear-executive