In a case of the death of a 7-year-old boy, the police investigations revealed a possible dog attack contrary to the witness testimonies. DNA investigations were carried out from hairs, saliva and bloodstains with 10 canine-specific STR loci by the use of fluorescently labelled multiplex PCR and the ABI PRISM 310 genetic analyzer. The analysis of one hair sample revealed one allele deviation from the profile of the putative Rottweiler perpetrator possibly caused by a mutation. The PCR fragments in question at the PEZ20 locus were sequenced and compared with the alleles detected in the Hungarian canine population and identified on a repeat number basis. The allele frequencies were determined based on typing of 242 genetically independent canine individuals from 72 breeds. The results suggested that two of the canine individuals could be the perpetrators.