The letters containing anthrax, sent in 2001 in USA, showed that pathogens and toxins can be effectively used for terrorist purposes. A new subfield of forensic science, called “microbial forensics”, has been developed. It is a new scientific discipline dedicated to collect and analyze microbiological evidence from a scene of crime. In addition to collecting and analyzing traditional forensic evidences, the microbial forensic investigation will attempt to determine the identity of the causal agent, as so as epidemiologic investigation, but with higher-resolution characterization. The tools for a successful attribution include genetically based-assays to determine the exact strain of isolate, aiming the individualization of the source of the pathogen used in a biological weapon. Following the 2001 anthrax attacks, genotyping of B. anthracis was done on 8 variable number tandem repeats loci (VNTR polymorphisms), with multilocus variable number tandem repeats (MLVA) method. In recent years some research groups have increased the VNTR markers number to 25 loci, while other groups have identified single nucleotide repeat (SNR) polymorphisms, which display very high mutation rates. SNR marker system allows the distinguishing of isolates with extremely low levels of genetic diversity within the same MLVA genotype.