A forensic genetic investigation reveals a captive origin for a wild alien population of raccoons in Italy.

Invasive alien species have extensively impacted the ecosystems, where they may affect the native biodiversity. The North American raccoon Procyon lotor is one of the most successful invaders in Europe since its introduction in the early twentieth century. In Italy, a wild population was first established in the North at the beginning of the 2000s following a local introduction event. A further self-sustaining population was reported ten years later in Central Italy. To support an official investigation by the authorities, who suspected a captive origin of the free-ranging raccoons in Central Italy, we used nuclear and mitochondrial DNA markers, combined with different statistical approaches, to characterise their gene pool and trace the source of the founders. Results revealed that founders came from a private zoo-park from which they had inadvertently escaped, soon establishing a reproductive population in the wild. Additionally, our mitochondrial DNA data were used to supplement the haplotype variability known to date in captive and wild raccoons from Europe, Asia and their native range. The comparisons allowed us to update previous networks based on the control region with a new mitochondrial lineage, which had not been detected so far.