BERLIN—On a rainy morning in a cemetery last month, Berlin’s hidden underworld briefly emerged from the shadows.

Nidal Rabih, one of the German capital’s most notorious criminals, had been killed by unidentified shooters days earlier, and his funeral drew nearly 2,000 mourners from across the country. Scores of police officers watched as bearded, beefy men in tracksuits and crew cuts filed by. Luxury cars with dark-tinted windows ferried older men to the graveside.

Mr. Rabih, a 36-year-old gang enforcer, was strolling in a Berlin park with his wife and three young children when he was shot eight times next to an ice-cream truck.

Recent months have seen a rise in killings and shootouts linked to what security officials say is a gangland war among Germany’s powerful crime syndicates. But for law-enforcement authorities in Berlin and around the country, Mr. Rabih’s slaying was the last straw, prompting an intensified crackdown on organized crime, with raids, arrests and indictments ramping up in recent weeks.

“A broad-daylight murder in a popular park packed with families is a whole new category,” said Martin Pallgen, spokesman of Berlin’s interior ministry.