If there was one good thing that ended up happening when it came to Murray's death, it was the fact that Neyla and Clockwerk didn't get the panic they'd envisioned; the truth (that somebody had attached a C4 explosive to the van) never was learned by the general public, and the spectators who had been present were easily fooled by the explanation that a tragic malfunction appeared to have taken place in the nitro system of the van, causing the deadly explosion. Unfortunately the other racers had to be threatened in various ways because they all knew that such a thing was impossible. Murray may not have been a intellectual genius, but it was well-known that he was second-to-none when it came to knowledge pertaining to auto mechanics. Furthermore, the racers knew that nitro by itself was highly unlikely to explode with sufficient force to obliterate an entire van and blast a crater into the racetrack. This would later come back to haunt both parties involved in the intimidation, which were the sponsor of the race and Interpol... the former of which would end up faring far better in the end then the latter.

Of course Interpol wasn't directly involved with the investigation of what had happened, as if they got involved nobody with half a brain would believe that this had been anything short of an outright murder... and then the questions and panic would start. However, those investigating the explosion were contacted discreetly, and given the "suggestion" that they shouldn't bother looking for anything out of the ordinary.

Interpol's efforts were only partially successful though; the investigators did a full investigation and discovered the presence of the "tracers" left behind by the explosive. However, Interpol was able to stop it from going any further as the investigators had to turn over the investigation and all the evidence they'd collected to Interpol. The discovery of a military explosive being involved immediately placed jurisdiction of the investigation squarely in Interpol's territory. Even if that hadn't been the case, those who had been in charge of the investigation up to that point didn't have the power either legally or politically to take the investigation any further. Interpol was ABLE to take the investigation further... they just DIDN'T take it any further.

Why on earth would they do that? Take your pick of reasons... all of them based squarely on fears and possibilities nobody (at least among those at Interpol who knew about this) wanted to entertain. It's not exactly an everyday occurrence when somebody's murdered via C4 explosive... and usually the victim is some political and/or military bigshot, not a stock van racer. Next was the obvious... nobody at Interpol wanted to take the chance that something like this would jog the memory of "Constable" Cooper, and for that matter some people at Interpol were still slightly skeptical that Cooper really had lost his memory. While there wasn't any evidence to prove that Cooper was pulling a con job on Inspector Carmelita Fox (and believe me, they searched for any such evidence quite thoroughly), if Cooper regained his memory and/or bolted...

Last but not least, it was a headache that some of the people at the very top didn't want to have to deal with. As far as THEY were concerned, it was no big loss to the world. "One less potential headache to deal with. Once a criminal, always a criminal." People like these are the reason that great tragedies occur; they think they are protecting the world by doing "damage control," but it only makes far worse by the deliberate ignorance of a greater potential threat. Of course, they couldn't hush up everything...