Hamelin was “in a state of shock” after the violent attack, city spokesman Thomas Wahmes said, while state parliament representative Tjark Bartels called it “unrestrained violence”.
Prosecutors in Hanover said that the man, who was accused of robbing a petrol station in nearby Aerzen with his brother on Tuesday, fell from the building while trying to escape.
Witnesses said that the 26-year-old managed to slip his handcuffs while talking with his defender before climbing out of the window.
The local Deister- und Weserzeitung newspaper quoted relatives who said that he had been pushed out of the window.
“The members of his extended family threw stones which they had torn up from the pavement at the police officers who were there to protect the clinic and attacked them with pepper spray”, police spokesman Jens Petersen said.
As well as injuring the 14 officers, the family – some of whom had travelled long distances from other states to be there - broke a number of windowpanes and the glass door of the clinic.
A small group of the attackers made it inside the clinic buildings by a rear entrance before being forced back outside by the officers, who summoned reinforcements from the whole region to deal with the onslaught.
Doctors tried to save the 26-year-old's life while the pitched battle raged between his relatives and the police outside, but he ultimately succumbed to his injuries.
Several family members are now being investigated for actual bodily harm, breach of the peace and property damage charges. None of them has yet been arrested.
Police from nearby Hildesheim are investigating the 26-year-old's deadly fall from the courthouse.