CNN  — 

Secretly shot video tells the story of an alleged spy ring at work in Bulgaria’s capital.

A woman in a white jacket arrives at the Russian embassy in Sofia; she is seen in animated conversation with someone unidentified. Inside a government office, a surveillance camera catches a man counting money at his desk, apparently the reward for his espionage. And in an intercepted phone call, the alleged leader of the group is heard telling an accomplice how his father cried when Stalin died. Then they talk money.

The recordings, made by Bulgarian investigators, were released on Friday as prosecutors announced charges against six Bulgarians – several of them senior or former defense officials – on suspicion of spying for Russia.

Prosecutors alleged that the group “posed a serious threat to national security by collecting and handing to a foreign country state secrets of Bulgaria, NATO and the European Union.”

They also released a memo allegedly written by the group’s leader, in a mixture of Bulgarian and Russian, setting out the spy ring’s priorities, which included gathering information on NATO meetings, EU policy towards Russia and intelligence on Ukraine and Belarus.

According to prosecutors, of particular interest to the spies was the recently inaugurated NATO Maritime Coordination Center in Varna, on Bulgaria’s Black Sea coast.

A woman leaves the Russian embassy in the Bulgarian capital, Sofia, with what prosecutors claim is a bag full of cash.

The group’s apparent unmasking came days before US Secretary of State Antony Blinken’s first visit to NATO – with Russia very much on the agenda - and amid signs that the Biden administration is intent on taking a tougher stance towards Moscow than that pursued by former President Donald Trump.

“The days of the United States rolling over in the face of Russia’s aggressive actions … are over,” Biden said last month.

A State Department spokesman tweeted last week that the US was “attentively watching” the Bulgarian investigation and that it “stands with Bulgarians against these malign activities.”