The operation described in this case can be described as a proactive investigation.
Explanation:
In addition to information about an alleged criminal activity gathered by intelligence-gathering or through witness reports, proactive investigation is carried out. There's no imminent threat to witnesses in these circumstances, which means investigators don't need to immediately respond.
The famous instance is terrorism or terror attack where the terrorist enters the region with full strategy by generating some motive to devastate an area, but immediately the police or military individuals start investigating on receiving even any doubtful news regarding the same.