The pilot and a crew member survived and seems to be not severe injured. On footage of the scene you can see both crawling over the roof of the building where this helo crashed. One other crew member and one person on the ground died.
This was a EC135, used worldwide. Footage show flames near the engine and later the tail broke. Why the tail broke is unknown at this point. Even it is unknown what the cause is of the fire near the engine.
The main question however is: why were they still flying, even if it was for a minute? The procedure for this type, and many other helos, is to land immediately if a fire persists - not just as soon as practicable. There were emergency landing options below the flight path.
Indications not clear? Underestimated how quickly this can go wrong? Exactly because of the risk of structural failure of the tail boom with an engine fire the procedures are what they are.
Probably it was unknown there was a fire in the engine because according radio communication the pilot reported an error with the mechanics, not a fire.
I am not familiarity with the procedure for mechanical errors in flight.