A Brazilian man arrested in Rio de Janeiro has admitted to killing 42 people since 2005.

Sailson Jose das Gracas, 26, was arrested by police on Wednesday after stabbing a woman to death.

In police custody he admitted to stabbing or strangling to death 37 further women, as well as three men and a two-year-old girl, and warned that he took pleasure in the murders and would kill again if released.

Agency Brazil reports that police are suspicious of his possibly “fanciful” claims, which would make him one of the most prolific serial killers in history. They went on to say that a thorough investigation is needed to verify his statements and if they are found to be true examine how police failed to catch him for a decade.

In O Globo, forensic psychologist Guido Arturo Palomba proposes that if the claims are true, then Sailson may be more likely to be a hired hitman than a psychopathic serial killer.