Both brakes failed, maybe because of very poor maintenance. Its not very common to have both brakes to fail at once, so maybe one of the brakes hadn`t worked since last service..
There was two service men in the windmill, trying to slow it down, but they couldn`t because of loosing the brakes. They heard strange noices and the mill went crazy. They left the mill and ran for their life...
There was gail force winds in DK at the time, that explains the speed...
The windmill company Vestas, will not give answers to the public right now..