Owlcat Games talked about the investigation mechanics in Warhammer 40,000: Dark Heresy.
In the game, the player takes on the role of an acolyte who does typical Inquisition work: receives a suspicion (rumor, strange report, recurring name) and begins an investigation. Each case is unique, and the consequences of decisions can affect both small groups of people and the entire Calixis sector.
The main part of the gameplay is built around collecting and analyzing evidence. This can include blood stains, burnt documents, unknown substances, symbols on walls, etc. Some clues are obvious, others require special skills or tools: terrain analyzer, event reconstruction, searching for hidden traces. False testimonies and false evidence are common; witnesses in the Imperium rarely tell the truth to an Inquisition agent.
Servo-skulls return to help the acolyte. There are several of them, each with its own set of functions: auspex scanning, substance analysis, psyker detection, image and sound recording, highlighting, and more.
Everything found is recorded in the "Detective Journal" — a separate interface where each case has its own tab with evidence, connections, and conclusions. The player connects the facts and builds theories. Companions sometimes suggest their interpretations.
When the investigation comes to an end, the acolyte prepares a report for the inquisitor: who is to blame, what evidence was found, what actions were taken. The report can be distorted — accidentally or intentionally. The blame may fall on an innocent person due to lack of data, personal dislike, or a desire to settle scores. The consequences of such decisions will affect the further plot.