Deid Mann was the victim in the second KG-8 incident. He was a staff member of the Cohdopian Embassy in the United States.
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Quercus Alba, Cohdopia's ambassador to the United States, was the leader of the smuggling ring, and he saw Mann as a threat once he submitted himself as a witness to the embassy's smuggling activities. In addition to this, the Yatagarasu had stolen a special key from the embassy and was closing in on its target, the mastermind of the ring. Alba tasked one of his agents, who was spying on the Yatagarasu as a mole, to neutralize both of these threats. To this end, "Calisto Yew", as the agent called herself, hired a hitman, Mack Rell, to kill Mann. However, he was caught on camera, and promptly arrested.
[Taken from his Ace Attorney Wiki page.]