The articles linked in reddit do say that the sisters expelled him. Obviously the journalists have no clue how things work in JW world. In other articles though, the explanation is definitely clearer. They do imply some type of revenge because the sisters as well as the perpetrator, a music teacher, were JWs. Whereby he was recently expelled.
It is obvious that he is the murdered because they captured him in his house where they found a computer that belonged to the sisters, dresses with blood of the sisters and the marker he used to write "Muerte a los testigos" (Death to the witnesses) in the victims' apartment.
A tragic situation.
Vivalavida