Apparently the asphericity is due to Zastrow (see [Cannon-Conner-Zastrow][1]). 

Also apparently the result that the higher homology groups vanish is [due to Zastrow][2], but his habilitation thesis never seems to have appeared. 


  [1]: http://www.sciencedirect.com/science/article/pii/S0166864101000050#
  [2]: https://mat.ug.edu.pl/~zastrow/nonanorn.ps