Ok when Dresden lets off the firestorm at Bianca's Ball he regrets all the people he killed. But only 11 bodies, all inhuman, were discovered. Human bone disintegrates at 1500 degrees Celsius. So Harry's "living fire" spell which targeted the vampires and burned the trees had to have burned that hot to have killed any humans. Wood burns at 300 degrees so it was definitely that hot. 300-1500 is a pretty massive range. What else has Harry burned? His flames have occasionally melted through walls but explosive force and wooden infrastructure make that less than helpful. He's melted asphalt before, but that starts to melt in the sun at a mere 50 degrees so it's not like its hard. I haven't tracked it down, but I think he may have melted stone once or twice, that's ~1200 degrees by googling so we're getting closer, but this is much later in the series. And steel melts at 1300 degrees, again much later in the series. So the question is, can GP Harry, having had a bunch of his power recently eaten by the Nightmare, throwing fury-based magic that almost kills him, cast a large aoe firestorm that burns 1500 degrees across its breadth (in order to disintegrate all the human bones)?
No way. The human bodies were removed from the scene during the firestorm since they weren't there after and they were there before. Someone Interfered, and Dresden broke no laws of magic that day. The question is, who could have had the motivation, power, and ability to do this?
Small note. It is mentioned that the flames rise 50-60 ft in the air, but this should not be attributed to a more powerful flame. If you've ever lit a medium to large Christmas tree you'll know that the flame can reach way higher than the tree itself, in my experience during a semi-controlled bonfire easily 30 ft. and these are taller trees ignited immediately.
Smaller note. In CD Harry casts a harpoon of blue fire in one of his most powerful and efficient displays of fire magic backed by the winter mantle at HWWBefore. He says it's hotter than anything this side of the sun, whose surface burns at 5000 degrees. However, even if Harry is right about this which I doubt, it's probably hyperbole, this is not a spell that GP Harry has the power or focus to pull off (more focus allowing the fire to be more concentrated and ergo hotter).