It's unusual for Agent Cho to be armed at work. But a crime is committed on the offices of the CBI during the episode "His Red Right Hand."
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Three members of the team look on his disbelief in this scene from "His Red Right Hand." Someone is dead in their office.
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In this scene from "His Red Right Hand," Jane is on the case of the person that committed a crime in the CBI offices.
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Isn't this adorable? The Mentalist character Wayne Rigsby and Grace Van Pelt lie together in bed.
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There's a good reason why Lisbon looks so shocked here: a murder has taken place inside the CBI offices.
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The Mentalist Season 2 Episode 8 Quotes

Bosco: They're Jane's people. They need watching.
Lisbon: I like to think of them as my people.
Bosco: Well, think what you like. I can't have them trying to pull some cheap stunt behind my back.
Jane: Well, we have a whole range of expensive stunts if you don't like the cheap ones

This is Red John's mistake.. he made a mistake and this is it!

Jane