I believe the presumption of innocence relates to criminal proceedings and not civil litigation. My question in regards to the criminal investigation is should there be any presumption as to responsibility before there is an accurate determination as to cause through a responsible investigation using the scientific method to reach a conclusion. In a criminal investigation, the investigator must make an accurate determination as to a cause before there is a person of interest. If there is a determination as to a person of interest prior to there being a factual finding as to the cause, is this not an indication that there is a bias on the part of the investigators, which could cause the investigation to over look other factors.

As to the civil terminology of interested party, there is a big difference. That is not in itself a declaration that a party is responsible for the incident, but just a notification to that company that their product is believed to be within the area where the fire originated, and you are giving them the opportunity to participate in the investigation to protect their interest.