Unlike Nuclear DNA which identifies one person uniquely, there have been cases where mtDNA or Y-chromosomeDNA have proven helpful. Certainly can narrow down the field of viable suspects.
Although, from the article (below), it is stated
"Due to multiple relatives having the same Y-chromosome profile, unique identifications are not possible from Y-chromosome analysis", the odds towards a particular suspect increase drastically when there are few relatives living in that area.
"Mitochondrial DNA (mtDNA) is a form of DNA that is transmitted from mother to child in a complete set; therefore, anyone in the maternal lineage will have the same mtDNA profile."
Y-chromosome DNA testing is a form of nuclear DNA testing that is specific to the male chromosome, also known as the Y-chromosome. This type of testing can be useful for sexual assaults, missing persons, and intelligence cases. The Y-chromosome is transmitted from father to son as a complete set; therefore, anyone in the paternal lineage will have the same Y-chromosome profile. Due to multiple relatives having the same Y-chromosome profile, unique identifications are not possible from Y-chromosome analysis.
DNA Casework — FBI