Information is power and there are some civil servants who like to have power. On top of that, the labyrinth of red tape behind which a series of documents can get lost, especially given the passage of time, is impressive. Thirdly, litigation paperwork is treated, in my personal experience, with a certain amount of care and weight that may or may not go alongside materials requested via freedom of information laws.
The simple fact of the matter is that he has alteady drawn attention to the documents he wants, or news agencies have done it for him. Whether he receives permission to sue at this point or not, he has at least gotten it noticed. That's not necessarily a loss.
Finally, I can't decide whether it is very jaded or quite naive to think that one man could turn the murder of over two dozen people into a farce. Come on, now.