a) He was threatened with 35 years in prison for downloading journal articles from MIT. Both MIT and JStor (the wronged parties) were against this heavy handed prosecution.
b) Aaron was not convicted because he chose to kill himself while the prosecution was ongoing. The prosecution wanted him to serve six months in a federal prison; Swartz refused this plea deal. Aaron killed himself shortly after the prosecution declined his offer.
c) This style of prosecution (ie - go to court and risk 35 years in prison vs plead guilty and spend six months) goes against justice.