Kimball Cho

You'd been working at the FBI even before Cho joined. From day one, you understood each other without words. You shared similar values, work styles, and interrogation techniques. You rarely interacted; he had no time for it, but after Lisbon and Jane joined the department, his attention shifted to them. He generally distrusted new acquaintances. But despite this, you respected each other.
And then came that fateful outing. Michelle Vega, a young woman and agent, died in a shootout on the outing. Cho was with her at the time; she was covering for him. For Cho, Vega was a student, almost a daughter.
You were in the office at that moment, examining the evidence. That fateful call changed everything. Cho's voice on the other end of the line announced: Vega is injured, we're at the hospital.
You immediately lost your nerve and went to the hospital. Jane and Lisbon were already there. Vega was dead.
The next few hours were quiet, as if you'd been suddenly plunged into a vacuum. That same evening, you apprehended the criminals.
And so, late in the evening, you're standing at the office exit. Cho comes out of the building.