(Capcom's primary storyline)
Mendoza was friends in high school with Wayne Li who would become his future coworker at Umbrella Corporation. He also had disagreements with Bryon Cartwright and appeared to have sought out his position.
Raccoon City Destruction Incident
During Operation: NESTWRECKER, the USS began shooting Umbrella employees in the facility. Having survived the attack with other scientists, for not being able to operate the bridge with the wristbands that have, Mendoza tried to find Cartwright in order to use his ID Wristband. In the meantime, he tried contacted Li to ask for his help due to the seriousness of the situation. Unknown to him, Li had already been killed and infected in the midst of the USS attack.
The other members of the greenhouse team, meanwhile, were tackling the Monster Plant they were working on, and made plans to kill it with poisons but, without Li's help, they failed to produce an effective herbicide. Amid the crisis, Mendoza found the Cartwright's ID Wristband, but Plant 43 became aggressive and outright attacked in the greenhouse area, a mouth-like flowerbud and smashing him to death against the reinforced glass window.