An appeals court has found that the mass surveillance of Americans’ telephone records exposed by Edward Snowden was illegal. In a ruling issued Wednesday, the U.S. Court of Appeals for the Ninth Circuit said the operation that secretly collected millions of Americans’ phone records was in violation the Foreign Intelligence Surveillance Act and could have been unconstitutional. Snowden, who fled to Russia after exposing the program in 2013, still faces U.S. spying charges. The whistleblower said on Twitter that the ruling vindicated his decision to go public with evidence of the National Security Agency’s surveillance operation. “I never imagined that I would live to see our courts condemn the NSA’s activities as unlawful and in the same ruling credit me for exposing them,” he wrote. After Snowden exposed the program, U.S. officials insisted the spying played a key role in fighting domestic terrorism, but the appeals court ruled that claim to be “inconsistent with the contents of the classified record.”