"So, you seem to know me. Been fantasizing about me, have you?"
In mid-1997, Coen was a Second Lieutenant in the United States Marine Corps with Force Recon. While opposed by the UN, the US was intervening in a civil war in Africa, and his squad was sent out to confront the guerrillas head-on at their base deep within a jungle. Dropped some distance a way, the march to the base was long and arduous. A fever spread among the men, and they were harassed by guerrillas. By the time they reached their destination, only four were left. When their target quickly turned out to be a village and not the guerrilla base, the squad leader ordered they massacre the villagers anyway so as not to come back empty-handed. Coen disobeyed orders, and was knocked out with a rifle-butt while the other three brought all twenty-three villagers into a circle to be shot.
Following the mission, rumours quickly spread about the operation, and a commission was established to investigate. Faced with the escalating scandal, they agreed to a cover-up, and Coen was blamed for the deaths owing to a temporary loss of sanity. He was taken to a psychiatric hospital for a further check up and found to be sane enough to stand trial. He was found guilty under Clause 1; Article 118 of the Uniform Code of Military Justice, and sentenced to death.[excerpt 1]
"Listen, little girl. If you haven't noticed, there's some pretty freaked-out things on this train. And I, for one, wanna get out of here. I don't think we stand a chance of doing it alone."
On 23 July, Coen was driven up through the Arklay Mountains en route to the Regason Base for his impending execution. During the trip, the vehicle was attacked by mutant leeches and crashed, with its MP occupants apparently being killed. Escaping out into the woods, Coen found Ecliptic Express, a train for Umbrella personnel which had stopped in the woods and was also occupied by mutants. While looking around, he met Rebecca Chambers, a S.T.A.R.S. medic who was out looking for him, being the suspect in the deaths of the two MPs. Coen persuaded her to cooperate with him in their effort to survive. The train soon began to run, restarted by Umbrella Security Service operators who were themselves infected by the leeches. With the train now out of the control, the two worked together to activate the emergency breaks. Though they were successful, they quickly ran out of track as the train came crashing into an underground railway station, itself beneath Umbrella's abandoned executive training center.
During their exploration of the building, the two uncovered evidence of illegal human research undertaken by Dr. James Marcus, the facility's director, having infected a number of children with a prototype t-Virus and performed torturous experiments on them. As they reached a cable car, Coen was attacked by a B.O.W. and fell down a ledge into an underground stream, where he was swept away to a water treatment plant. He awoke some time later, having been found by Chambers. There he found himself against the skeletal remains of a number of child test subjects. Both were monitored by Queen Leech, believing it was a resurrected James Marcus, who had sent various creatures to subdue them. Walking in on Queen Leech in human form, the creature boasted its resurrection before attacking. The two managed to temporarily subdue the creature, only to discover that a self-destruct protocol had been activated, caused by William Birkin to contain the outbreak. Matters became even more complicated when the leech mutated into its second form. During the final battle, Coen fended off the Queen Leech while Chambers opened the roof and exposed the leech to sunlight, thus making it vulnerable to attack.
Realising the creature's weakness, Coen acted as bait, whilst Chambers opened the roof further until there was no shade left for the creature to hide in. Coen proceeded to deliver a final shot with a powerful Magnum revolver, which instantly destroyed Queen Leech. Together he and Chambers escaped the crumbling facility. In the wake of the destruction, Chambers allowed him to escape, by telling her authorities that he subsequently perished in the Arklay Mountains after their first encounter, keeping his dog-tags as proof. The two bid farewell as Chambers heads to meet her comrades while Coen escaped and was never to be seen again.
Upon returning to Raccoon City after the Mansion Incident, Chambers filed a report falsely claiming that Coen had died during the initial attack on the van, keeping her word.[excerpt 2] According to the report, Bravo Team was forced to leave Coen's body behind at the site of the MP vehicle. She went on to request a suspension of the case. As of September 1998, when the Raccoon City Outbreak occurs, it is unknown if this suspension was carried out. However, any police records of the case are presumed destroyed following Raccoon City's destruction. Billy Coen's current whereabouts are unknown.