The EFF will rely on the same evidence its civil suit does -- wiring documents and a signed declaration from former AT&T engineer Mark Klein. Klein alleges that AT&T siphoned off internet traffic into a secret room in San Francisco controlled by the NSA. (See Wired.com's publication of the Klein documents that remain under partial seal in federal court.)
Though the EFF didn't want to sue the government originally, the amnesty issue forced their hand, according to Cohn.
"If it was illegal for AT&T to turn over the data, then it was illegal for government to receive it," Cohn said.
Cohn admits the government has many sovereign immunity defenses that can protect it from lawsuits, but says they aren't insurmountable and that the program clearly violates the Fourth Amendment.
As for the unexpectedly long-lived suit against AT&T, the government and the EFF are discussing when and how the government will attempt to have the case dismissed using the amnesty provision. The EFF wants to challenge the legality of the amnesty before it is actually applied, while the government prefers to have the case dismissed first -- then have the EFF fight the dismissal
Let's hope EFF wins.