  The daily routine of criminal investigators consists of a thorough analysis
of highly complex and heterogeneous data of crime cases. Such data can consist
of case descriptions, testimonies, criminal networks, spatial and temporal
information, and virtually any other data that is relevant for the case.
Criminal investigators work under heavy time pressure to analyze the data for
relationships, propose and verify several hypotheses, and derive conclusions,
while the data can be incomplete or inconsistent and is changed and updated
throughout the investigation, as new findings are added to the case. Based on a
four-year intense collaboration with criminalists, we present a conceptual
design for a visual tool supporting the investigation workflow and Visilant, a
web-based tool for the exploration and analysis of criminal data guided by the
proposed design. Visilant aims to support namely the exploratory part of the
investigation pipeline, from case overview, through exploration and hypothesis
generation, to the case presentation. Visilant tracks the reasoning process and
as the data is changing, it informs investigators which hypotheses are affected
by the data change and should be revised. The tool was evaluated by senior
criminology experts within two sessions and their feedback is summarized in the
paper. Additional supplementary material contains the technical details and
exemplary case study.
