Final answer:
Chemically testing two similar white powders can show they are the same substance, but it doesn't prove they come from the same source. Forensic scientists use more specific analytical techniques to conclusively link samples. For common substances, additional evidence is required to establish a definite connection.
Step-by-step explanation:
The question touches upon the challenge of individualizing a substance, in this case, a white powder, by comparing two samples to determine if they originate from the same source. While similar powders can be chemically tested to prove they are the same substance, this does not necessarily mean they come from the exact same bag or source. Many substances, such as salts and sugars, can look identical but come from different sources, which is a concept chemists and forensic scientists are very familiar with.
When dealing with forensic evidence, it's essential to consider that substances can have the same chemical composition and still be from different batches or sources. Forensic analysts often require more specific analytical techniques or evidence, such as unique markers or impurities, to link a suspect's sample to material found at a crime scene conclusively. Therefore, the presence of similar substances on both a suspect and a victim doesn't irrefutably prove they came from the same bag; additional investigation is required.
For example, when conducting a DNA analysis, forensic scientists can pinpoint an individual based on the unique genetic makeup found in the sample. This level of individualization is not achievable with common substances like white powders unless they contain distinctive markers or characteristics.