GEOGRAPHY: At least one of the hacker groups attacking the DNC appeared to cease operations on Russian holidays, and its work hours aligned with a Russian time zone, cybersecurity company FireEye concluded in a report.

LANGUAGE: The hackers also left an obvious digital fingerprint, one cybersecurity expert said, perhaps on purpose: a signature in Russia's Cyrillic alphabet.

FORENSIC EVIDENCE: After a different batch of hacked Democratic emails was released last month, a wide spectrum of cyber-security experts concluded that it was the work of Russian intelligence agencies through previously known proxy groups known as COZY BEAR or APT 29, and FANCY BEAR or APT 28. "We've had lots of experience with both of these actors … and know them well," according to the DNC's own contract cybersecurity firm, Crowdstrike, which blogged that one of the two groups had already gained illegal access to the White House, State Department and even the military's Joint Chiefs of Staff.

MOTIVE: Given their mutual and very public bromance, Putin would much prefer a Trump presidency to a Clinton one, and the timing suggests the leak was timed for maximum embarrassment to the Democrats and their presumptive nominee. Clinton campaign manager Robby Mook said the campaign was told by cyber experts that Russian hackers stole and released the emails to help Trump. "I don't think it's coincidental that these emails were released on the eve of our convention here," said Mook, "and I think that's disturbing."