Passers-by reported in the morning that a man was behaving strangely and carrying a long knife in the Neptune fountain, near Berlin's city hall, police spokesman Stefan Redlich said.
Officers tried to persuade the man to put the knife away, but instead he started cutting himself. A policeman climbed into the water to try to stop him, whereupon the man advanced on the officer with the knife.
The man was shot by that officer after he ignored calls to back off. He died in an ambulance shortly afterward.
An autopsy determined that the man died as a result of being shot through the lung, Martin Steltner, a spokesman for local prosecutors, told the dpa news agency.
Police said the man was believed to be a 31-year-old Berlin resident, but didn't release his identity.
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