And seriously, what's the best practice to prevent such cases, when you hold/have access to significant amount of bitcoins? Sure you could hide your private key (or part of it) in some secure place outside of your home, but then the risk of you (or your family) getting tortured or even killed increases. Well organised group as described above unlikely would be happy to leave with nothing.
I heard about this case recently on another forum and it really made me sad. But one thing to consider here is that how can anyone one know of your Bitcoin investments. Provided you do not show off your earnings or talk about it to relatives and friends, there are very less chances of this getting in notice of criminals. I think it is better to remain secretive about Bitcoin investments to remain on the safe side. Finally, I hope those criminals are exposed and dealt with.