The FBI Laboratory routinely types 13 short tandem repeat (STR) loci in determining DNA profiles. In many forensic cases routinely processed, a sufficient number of highly polymorphic markers are used, so that the reciprocals of random match probabilities exceed the world population. This enables the forensic analyst to report that a particular individual is the source of an evidentiary sample with reasonable scientific certainty; however, source attribution should not be confused with "uniqueness." When making a source attribution, there is often little need to establish that a DNA profile is found in only one person in the entire world. Instead, source attribution should be considered in the context of the given case. Rarely would case circumstances require that the entire world's population be considered as the pool of potential contributors of an evidence sample. In some cases, it may be relevant to consider that a relative of the suspect may be in the pool of potential contributors to the sample. If a relative had access to a crime scene and there is reason to believe that he/she could have been a contributor of the evidence, then a reference sample should be taken from the relative. When a suspected relative cannot be typed, the conditional probability that the relative has the same DNA profile as the accused can be calculated. The current core 13 STR loci should be more than sufficient to resolve the question as to whether a relative carries the same DNA profile as the accused. 10 references