It's a canny move, your attempt to focus the attention of your people on the possible cause of this death. Plus, it's true that the killer—man, woman or monster—may still be among you.
Only two low-level security guards are present, but they follow your instructions. One moves to block the building's main entrance; the other closes and locks a door behind reception that leads to a side exit from the building. Better yet, the rest of the people in the lobby allow them to do so without obstruction. They trust that you know what you're doing.
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