(Capcom's primary storyline)
The liaison was a man who Ada Wong was originally assigned to meet after acquiring a G-Virus sample. Unfortunately, he lost his will and killed himself at the Apple Inn before Ada could get to him.
He was a white haired man and was wearing a black suit at the time of his death.
While Ada refers to the man as her "contact" in the localization, the Japanese script more closely refers to the man as "連絡員" - her "liaison".