A supposed insider from the Federal Security Service (FSB) says that Putin’s conquest of Ukraine has no chance of victory. The source claims Moscow could not properly assess the level of resistance from the Ukrainians and the response from the international community.

“No one knew that there would be such a war, so no one prepared for such sanctions,” the letter said. “It’s just that there is no option for a possible victory.”

The 2000-word letter from the FSB whistleblower was published on Facebook last week by Vladimir Osechkin, founder of the Russian human rights watchdog “Gulagu.” The text was later assessed by Christo Grozev from Bellingcat, a Netherland-based investigative journalism group. Grozev wrote in a tweet that he had shown the document to two of his FSB contacts, who confirmed the letter’s legitimacy.

“I showed the letter to two actual (current or former) FSB contacts, and they had no doubt it was written by a colleague,” Grozev wrote. However, he also shared that he had doubts about the authenticity of the document as Ukraine has leaked fake FSB letters before.