A permanent “kid genius,” Mr. Swartz had often put his skills to the task of making information more accessible. At 14 he was a co-creator of RSS, a tool that allows online content to be distributed, and then made a tidy sum as one of the creators of the social-news site Reddit, now part of Condé Nast.

But even before, and certainly after, he crusaded for open access to data. His projects include a range of influential efforts like the Internet Archive, Creative Commons, Wikipedia and the Recap collection of legal documents.

He also began more traditional projects for subjects he took an interest in. At 19, he volunteered to upload the archive of a defunct magazine he loved, Lingua Franca. In 2005, he called up the writer Rick Perlstein to offer to create a Web page for him after reading a book of his he liked.

“I smelled a hustle, asking him how much it would cost, and he said, no, he wanted to do it for free,” Mr. Perlstein wrote in The Nation over the weekend. “I thought: ‘What a loser this guy must be. Someone with nothing better to do.’ ” Mr. Perlstein writes that he ended up becoming friends, and he sent chapters of his next book, “Nixonland,” to Mr. Swartz before he showed them to anyone else.

Mr. Swartz outlined his views in the manifesto: “It’s called stealing or piracy, as if sharing a wealth of knowledge were the moral equivalent of plundering a ship and murdering its crew. But sharing isn’t immoral — it’s a moral imperative. Only those blinded by greed would refuse to let a friend make a copy.”

And he said the stakes were clear: “We need to take information, wherever it is stored, make our copies and share them with the world. We need to take stuff that’s out of copyright and add it to the archive. We need to buy secret databases and put them on the Web. We need to download scientific journals and upload them to file sharing networks.”

Still, even many of his allies concede that Mr. Swartz’s passion for free information may have taken him too far in the Jstor downloads. According to the government’s indictment, in September 2010 Mr. Swartz broke into a computer-wiring closet on the M.I.T. campus; when retrieving a computer he connected, he hid his face behind a bicycle helmet, peeking out through the ventilation holes. At the time, he was a fellow at the Edmond J. Safra Center for Ethics at nearby Harvard.