Forensic Questions For A Mystery Story

by Rebecca
(Chile)

Before I ask, let me just say that this question has no nefarious applications. The situation I'm asking about is completely fictional (for a mystery book I'm working on) and I would like to have a better understanding of the likely forensic evidence that could be used as clues.

I would like the story to have an authentic feel and so if anyone could help me get my clues straight, I'd really appreciate it.

Question: If a murder victim were to have been injected with snake venom, are there any common species whose venom might induce a coma (and how quickly), and if so, could this be discovered with a toxicology report (and is there a name for this type of report and would it need to be requested by the investigating officer)?

Now if this were to occur in a laboratory and someone were to have created a laboratory fire or explosion and the body were to be burned, would the poison still be detectable? Would any lacerations (such as an injection site or even a snake bite) be discoverable under close examination? Are there any chemicals that might be in a chemist's laboratory which could be used to fake an accidental fire or explosion? If so, what is this chemical's usual applications?

If you know the answer to one or more of these questions, please help me choose realistic details. I'd deeply appreciate your input.
Thank you so much.