Of the seven murders and three attempted murders finally attributed to de Berk by the court, the court considered two of them to be proven by medical evidence. According to the court, de Berk had poisoned these two patients. The court then applied a so-called chaining-evidence argument. This means that if the several attempted or actual murders have already been established beyond reasonable doubt, then much weaker evidence than normal is sufficient to establish that a subsequent eight "suspicious incidents" are murders or attempted murders carried out by the same defendant.