There has been a TV program about the collision as well as the official report. The Russian killed the wrong person.
Both make it quite clear that Swiss controller personally was not at fault but his company was. The shortcomings in the control centre that night were critical to the collision occurring.
In summary there was engineering work being conducted that night that removed most of the controllers telephone connections as well as the warning system of an impending collision. He was also distracted by having to work another aircraft that was on approach elsewhere and because of the telephone being disconnected he could not call the other controller who was in the rest room at the time.
The final hole in the Swiss cheese scenario (please excuse the pun) was that the controller did recognise the danger before the collision and called on the Russian aircraft to descend just after the TCAS in that aircraft had called for a climb. The DHL aircraft TCAS had called for a descent. The Russian crew obeyed the controller rather than the TCAS. The controller was not aware that the TCAS had activated.
The rest is, as they say, history.