Before you can take out or kidnap a rival, you first have to find him. The detective bureau is your tool for that: you hire detectives to track down players. On top of that, the bureau offers a calculator to estimate the outcome of an attack before you strike.
Hiring a detective is a requirement for both murders and kidnappings. You put together an investigation:
Once your detective finds the target, they track them for a while in that city — exactly the window in which you can strike. Costs scale with the tier and with the target's rank.
The bureau also offers a murder simulation (for donors): you enter the details of a hypothetical attack — ranks, bullets, weapon, protection, bodyguards, vigilance — and get an estimate of the damage on both sides. This lets you test-run an attack before committing real bullets and risk. The simulation uses the same formula as an actual attack.
Remember that tracking works both ways: if you choose the fast method, your target learns that a detective is on them and can hole up or switch to Bunker vigilance. Timing and discretion determine whether your attack succeeds.