Russian Embassy
© Getty Images / Carsten Koall
A person walks past The entrance to the Russian Embassy on December 6, 2019 in Berlin, Germany.
When a Chechen exile was shot dead in a Berlin park last summer it strained relations between Germany and Russia. A new report suggests his alleged killer may have been trained by Russia's Federal Security Service (FSB).

The joint investigation from Germany's Der Spiegel magazine, the US-government funded Bellingcat website and Russian outlet The Insider claims to have obtained the phone records of "Vadim Krasikov," which they say is the real identity of Vadim Sokolov, the man German police accuse of carrying out the murder of Zelimkhan Khangoshvili.

Khangoshvili was regarded as a terrorist by Moscow for his role in conflicts in the Caucasus during the early 2000s. He moved to Germany after apparently surviving an assassination attempt in the Georgian capital Tbilisi in 2015. The deceased was born in Georgia and previously served in its military.

According to the probe, in 2019 Krasikov/Sokolov visited training facilities belonging to the FSB's Special Purpose Center at least eight times. The last trip supposedly took place just a few days before he traveled to the European Union. In April 2019, the investigators contend Krasikov/Sokolov spent four days at an FSB base near the village of Averkievo, which is used as a shooting range. He also supposedly twice visited the Moscow building where the FSB's anti-terror center is located.

The team's research also asserts that Krasnikov/Sokolov traveled to Bryansk, near the Ukranian border, to pick up a passport before his departure. They say one of his regular contacts was Eduard Bendersky, said to be "chairman of the Vympel Charitable Fund For Former FSB Spetsnaz (Special Forces) Officers."

From February to August 2019, the group alleges the two men spoke on the phone at least 20 times, with the frequency increasing as time passed. Bendersky told The Insider he didn't know Krasikov/Sokolov.

Khangoshvili was killed in the German capital's Kleiner Tiergarten Park last August, while traveling back from a mosque. Soon after, police detained the suspect, who holds a passport under the name of Vadim Sokolov.

Der Spiegel is Germany's most famous news magazine, The Insider is edited by Roman Dobrokhotov, a Russian liberal opposition activist, and journalist who worked with numerous Moscow titles, and also contributed to US state broadcaster RFE/RL. Bellingcat's founder Eliot Higgins was previously a 'fellow' at pro-NATO pressure group Atlantic Council, which is funded by the British government, branches of the US military and various American defense contractors. Russia's foreign minister Sergei Lavrov has accused Bellingcat of being a front for Western intelligence services attempting to manipulate public opinion.

Berlin's Foreign Ministry believes Russia hasn't fully cooperated with the investigation of Khangoshvili murder. It expelled two Russian diplomats in December. Moscow retaliated by kicking out a pair of German embassy staff. President Vladimir Putin denied the involvement of Russian special services in the murder, and claimed that Khangoshvili was involved in fighting in the Caucasus on the side of terrorist forces. Putin called him a "cruel and bloodthirsty person."

"In just one of the attacks in which he took part, he killed 98 people. He was one of the organizers of explosions in the Moscow metro," said the President. Putin's first point referred to a June 2004 attack on Russian security forces in Ingushetia and Dagestan, in which 98 military personnel were killed. His second reference was likely to the 2010 Moscow metro bombings when 40 lives were lost, with over 100 people injured. No specific evidence was presented.