Well, let's take a look at arson and arson investigation as I'm on a real crime scene roll. It's funny but some of the information I've found, such as how bright red the blood and organs can look when someone dies of carbon monoxide poisoning, could be useful even in my fantasy world. After all, if I mention the red flames and black smoke of a cooking oil fire, I'd have gotten it wrong. It just goes to show that all research is good research!
An arson investigation begins with an exterior examination where the people involved will talk to the first responders, witnesses, and whomever called the alarm. They pay attention to the people present at the scene or even those who have risked themselves to save a life as vanity fires from wannabe heroes are surprisingly common. They try to learn what sort of smoke and flames were released in the early stages of the fire as that can give a lot of information. Red flames are cooler and white fires are the hottest at around 2500 degrees celsius. Since arsonists generally start fires with accelerant, oddly hot fires can suggest foul play.
Other than temperature, what can flames / smoke reveal?
Well, I'm glad you asked! Here's an example: White smoke with a white or light yellow flame indicates gasoline, while brown smoke with a deep yellow flame suggests a cooking oil fire.
The investigators then do an internal investigation where they try to determine the point of origin which is the place the fire started and how it spread. A V-shaped burn pattern on a wallcan hint at the starting point because as heat rises it spreads out from that point. Wooden beams and heavy wood furniture can be used to identify the fire path as damage can occur more on one side than the other. Charred wood looks like scales and one can measure the amount of char to see how long the wood was exposed to high heat. The closer this bit of wood was to the point of the origin, the deeper the char and the smaller / closer together the scales. Window glass tends to discolor from soot but the hotter the fire, the less soot. Incadescent light bulbs normally shatter in heat but, if it has somehow remained intact, it will melt and curve toward the head source. The same effect can be found sometimes with glass salt shakes and even plastic milk jugs.
The examiners will try to rule out possible accidental causes, such as exposed wiring of the stub of an unattended candle. They also look for obvious signs of foul play such as suspicious stains that might be tested for accelerant or long lines of ash that may indicate "trailers" (lines of paper, gasoline-soaked towels or ropes, etc. that are designed to spread the fire). The debris is also carefully sifted for any signs of an igniting device.
Hydrocarbon Indicators can be used to detect accelerants. They are about the size of a flashlight and will report any traces of an accelerant. Sniffer dogs can also locate accelerants though a dog's nose won't stand up in court so the investigator needs to get a sample from the location and get it tested in a laboratory. These samples must be kept in clean paint cans-style equipment since plastic bags can react chemically with the accelerant.
So there you go, a quick look at arson investigations. Hmm, what should I research next? Advanced states of decomposition? Stages of child development? Hmm.... Any ideas?