Edward Snowden, in a series of tweets Monday morning, called out the U.S. government for not providing evidence that Russia was responsible for the hack on the Democratic National Committee.

Hillary Clinton’s aides have publicly pushed the blame for the leak on hackers working for the Russian government.

The former National Security Agency contractor who leaked sensitive documents on U.S. surveillance operations argued that during the 2014 Sony hack the FBI provided evidence that North Korea was responsible for the hack and that if it does know that Russia is responsible, the agency should condemn it.

“The FBI is investigating a cyber intrusion involving the DNC and are working to determine the nature and scope of the matter,” the FBI said in an official statement. “A compromise of this nature is something we take very seriously, and the FBI will continue to investigate and hold accountable those who pose a threat in cyberspace.”

“Evidence that could publicly attribute responsibility for the DNC hack certainly exists at #NSA, but DNI traditionally objects to sharing,” said Snowden in one of the tweets.

Snowden also suggested that this kind of transparency could protect the United States from other attacks.

“This is the only case in which mass surveillance has actually proven effective. Though I oppose in principle, it is a mistake to ignore,” read one of Snowdens tweets, adding, “Defensive capabilities should be aggressively public.”

Read all of Snowden’s tweets below:

If Russia hacked the #DNC, they should be condemned for it. But during the #Sony hack, the FBI presented evidence. https://t.co/SG7er8VDRD — Edward Snowden (@Snowden) July 25, 2016

Even if the attackers try to obfuscate origin, #XKEYSCORE makes following exfiltrated data easy. I did this personally against Chinese ops. — Edward Snowden (@Snowden) July 25, 2016

Evidence that could publicly attribute responsibility for the DNC hack certainly exists at #NSA, but DNI traditionally objects to sharing. — Edward Snowden (@Snowden) July 25, 2016

The aversion to sharing #NSA evidence is fear of revealing “sources and methods” of intel collection, but #XKEYSCORE is now publicly known. — Edward Snowden (@Snowden) July 25, 2016

Without a credible threat that USG can and will use #NSA capabilities to publicly attribute responsibility, such hacks will become common. — Edward Snowden (@Snowden) July 25, 2016

This is the only case in which mass surveillance has actually proven effective. Though I oppose in principle, it is a mistake to ignore. — Edward Snowden (@Snowden) July 25, 2016