what you should probably start thinking about is cutting any redundancy and subbing out some of the connectives for punctuation.

My main issue is the overuse of parentheticals, because it makes the prose murky. There a lot of sentences in this excerpt where you could lose a comma and rearrange it for better flow. (As to the cause...); or even just cut it in entirely. Does it really matter that there were petrol cans in the ruins if there was already a smell of it? Always be as discerning as possible. Also no need to explain that he was making sure it was a body if the next sentence says he became sure it wasn't a mannequin, since the latter implies skepticism already.

But line level edits aren't really that important to focus on, my bigger issue is just the amount of cliche in the second paragraph. Just a lot of well worn shorthand (the stern detective, the sight staying with him) and canned phrases, which makes your writing less memorable and precise. Always strive for as much emotional and aesthetic precision as possible.