Jeffrey Cahn was an officer of the department of fish and wildlife.
In 1999, he investigated an animal escape on a cargo ship, the T'ien Kou. His team searched the whole ship and reported to Fox Mulder and Dana Scully that he did not find any evidence of an animal on the ship. He also spoke to the animal's supposed captor, Ian Detweiler.
When his friend, Frank Fiedler, was killed, he vowed to kill the animal himself and made it known to everyone. Detweiler overheard him and warned him not to do so, or he would be killed.
Cahn answered a call at James Riley's veterinary hospital. In the dark room, he shot quickly and shot Detweiler, though it was in the form of another dog and so it seemed he had shot the wrong dog.
Later, back on patrol, Mulder called him about the drug Detweiler received from the hospital. However, when he got in his car to head over, he was attacked by Detweiler as the wanshang dhole form, already inside. He did not die immediately and got to a hospital. Unbeknownst to him, Detweiler was waiting in the hospital room for him to wake up. (TXF: "Alpha")