When statistically related to child sexual abuse (CSA), background information can assist decision-making in investigations of CSA allegations. Here, we studied the use of such background information among Finnish police officers. We analyzed their ability to identify and interpret CSA-related and -unrelated background information both when placed in mock scenarios and when presented as separate variables. We also measured the ability to correctly estimate the base-rate of CSA allegations being true based on such background information. In the context of mock scenarios, officers were better in discarding CSA-unrelated variables than in identifying CSA-related ones. Within-subject performance across different scenarios was, however, not consistent. When information was presented as separate variables, officers tended to incorrectly consider many CSA-unrelated variables as CSA-related. Officers performed well in recognizing whether CSA-related variables increase or decrease CSA risk. Finally, officers were inaccurate in identifying variables that are CSA-related only for boys or only for girls. When asked to estimate the CSA probability of mock scenarios, participants were accurate only in assessing low-probability cases, and this was not associated with the ability to identify CSA-related and -unrelated variables. We conclude that police officers would benefit from more training in using background information and from using available decision-making support tools in the context of investigating CSA allegations.