Hi all,
I'm writing an urban fantasy story where the mc is investigating a 12 year old case where a laboratory was destroyed by two explosions. At the time, there was a cover up, and it was ruled accidental. The mc discovers by looking at records and interviewing people from the time that the explosions were deliberate sabotage/acts of terrorism. The perpetrator of them is a magic user, but part of what I want to do is make that not obvious right away. I am so not an expert when it comes to fires and bombs, though, so there's a lot I need help with to ground this fantasy in some believable reality.
One person says that the research they were doing in the lab did not involve combustibles, so that's the first thing that piques the mc's interest. However, the person who says this will turn out to have been lying about several things, so this detail doesn't have to be true.
1) What would indicate that explosions were deliberate? I'm thinking there would ordinarily be an accelerant, but maybe the absence of this is what would indicate that magic was involved? Assuming this is the case, what would the evidence look like without the accelerant? I have no preferences in terms of the type of bomb employed, although it couldn't be too obviously a bomb since there was a successful cover up after the fact.
2) What other kinds of evidence would suggest an impossible scenario (in other words, magic)? If you were watching a movie or a tv show, what would you see that would have you saying, "No way this could really happen"?
3) What chemicals would any typical lab have that are in fact combustible? I'm thinking I can send my mc after a red herring with that, if he asks someone who survived the blasts and they tell him there were such chemicals in the lab.
4) Do you have any other thoughts about how these explosions (there were two, though later the cover up tried to say there was only one) might have played out that would allow for a cover up and for my mc to uncover the truth 12 years later?

Thanks for any and all advice and suggestions, I really appreciate it.