Police have arrested a 49-year-old suspect from Russia's Chechnya republic over Friday's murder of the man media identified only as Zelimkhan K., 41.
The killer had approached his victim from behind, as he was on his way to a mosque, shot him twice and fled by bicycle in what one witness described as an “execution” style killing.
Police divers later recovered a Glock handgun, a wig and the bicycle from the nearby Spree river, reported Bild am Sonntag newspaper.
A large sum of money was found in the home of the suspect, according to Tagesspiegel daily.
The victim was reportedly a veteran of the Second Chechen War (1999-2009) who later joined a Georgian anti-terrorist unit.
In 2012, his unit engaged in an operation against militants holding hostages in the Lopota gorge near the border with Russia's Dagestan republic.
German media said the murder was believed to be a revenge killing related to the victim's military past.
One of his sons said Zelimkhan K., a father of five, had survived four previous attempts on his life, the most recent in 2015 in Tiflis, Georgia, B.Z. daily reported.
For the past few years Zelimkhan K. had been living in Berlin under an assumed identity.
German police had, meanwhile, also listed him a potentially militant Islamist for reasons still unclear, Bild reported.