Hundreds of people demonstrated in the western German cities of Mannheim and Heidelberg on Tuesday evening after a man died during a police operation.
Many more demanded an investigation into what caused the death of the 47-year-old man who was stopped by police in central Mannheim on Monday.
When the man refused to cooperate, the police officers overpowered him, the Baden-Württemberg state office of criminal investigation (LKA) and the Mannheim public prosecutor's office said.
In videos shared later online, one officer appeared to hit the man in the head.
The LKA said officers deployed the use of force, but did not elaborate.
The man then collapsed and was resuscitated, but later died in hospital. It was not initially clear why the man suddenly collapsed, and his body was taken for further examination.
An autopsy is scheduled for Wednesday and the results are expected by the end of the week.
The public prosecutor's office is investigating the two officers involved for bodily harm resulting in death while on duty.
On Tuesday evening, the police labour union (GDP) said it was still unclear what had caused the man's death. While concrete information was yet available, according to the union, it did say that the reactions seen online were excessive.
More than 300 people took to the streets to demonstrate against police violence in Mannheim and Heidelberg on Tuesday evening, police said. In Mannheim, some laid flowers and at the site where the man died, someone wrote, "police murder."
The rallies on Tuesday were the second time people protested, after some 100 to 150 people gathered on Mannheim's market square on Monday evening. Some held signs accusing the police of racially motivated violence.
The LKA tweeted that the deceased man was "NOT a Turkish citizen" in a disclosure intended to "prevent false reports." The man's nationality was not disclosed.
Police said earlier that a doctor at Mannheim's Central Institute of Mental Health had called about the man, who was a patient, and said he needed help. Two officers and the doctor then searched for the man, eventually finding him in the city centre.
