Three people have previously been arrested on suspicion of murder and attempted murder.
"There are many witnesses to the incident and there are still many interrogations to be held," says senior prosecutor Sonja Seligmann in a press release.
Two men were taken to hospital by ambulance following a brawl at a swimming pool last week. One of the men later died from stab wounds. The incident was described as a verbal altercation that escalated into a physical altercation.
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