When submitting evidence for analysis, which type is generally least useful?

Biological samples are generally considered the least useful type of evidence when it comes to arson investigations. This is primarily because biological samples, such as blood or bodily fluids, do not directly correlate with the cause or manner of a fire. While they can provide insights in certain criminal investigations, their relevance is limited in the context of arson where identifying accelerants, ignition sources, and fire patterns takes precedence.

The other types of evidence hold more substantial relevance in arson cases. For instance, solid debris can provide critical clues about the materials involved in a fire, allowing investigators to analyze potential accelerants or evidence of fire anomalies. Gas samples can be even more significant as they can help identify specific chemicals used to ignite a fire, aiding in determining the fire's cause. Witness accounts, while subjective, can provide essential information regarding fire behavior, observations of suspicious activity, or the circumstances leading to the fire's inception, making them a valuable component of the investigative process.

Thus, while biological samples may have their place in different investigations, they typically do not offer the same level of utility and direct relevance to establishing the characteristics and causes of arson compared to solid debris, gas samples, and witness accounts.