It is now widely accepted that forensic DNA profiles are rare, so it was a surprise to some people that different people represented in offender databases are being found to have the same profile. In the first place this is just an illustration of the birthday problem, but a deeper analysis must take into account dependencies among profiles caused by family or population membership.
"The rarity of DNA profiles." Ann. Appl. Stat. 1 (2) 358 - 370, December 2007. https://doi.org/10.1214/07-AOAS128