You need to provide a lot more information including the "several factors" that are inhibiting an investigation. Explain your fire scene. Was the fire inside or outside? What were the weather conditions? Why do you think it is a case of arson? Have you examined ALL potential ignition sources, i.e. discarded smoking material, candles etc. This is much more complicated than simply taking one piece of information and forming an opinion that it is arson case. If anyone is going to assist we will need additional information.