revenge against Umbrella. After temporarily defeating it, Billy and Rebecca attempt to escape to the surface via a lift, just as William Birkin trips the facility's self-destruct mechanism. Pursued by Queen Leech, the pair eventually kill it and escape before the facility is destroyed. Following their escape, Rebecca notices the mansion that Marini mentioned and prepares to head for it. Before she does, she assures Billy that her police report will list him as another casualty of the incident. Thanking her for his freedom, Billy departs as Rebecca heads towards the mansion to seek out the whereabouts of her fellow Bravo Team members (seen in Resident Evil). Development While the original Resident Evil (1996) was still in development, the idea for a prequel came up shortly after the 64DD peripheral for the Nintendo 64 was announced in 1995. Following the 64DD's low sales four years later, Capcom developed Resident Evil Zero as a cartridge-based Nintendo 64 game. Capcom started development on the Nintendo 64 version in mid-1998, one of many Resident Evil games being developed at the time. One of these was Resident Evil – Code: Veronica (2000) which was taking full advantage of the capacities of the GD-ROM format. The Nintendo 64 cartridge could only store 64MB of data, one tenth that of a traditional CD-ROM. For these reasons, the team approached Resident Evil Zero with different ideas for gameplay and visual design that would function better with less storage space. After the script had been completed in early 1999, the production of a Resident Evil game for Nintendo 64 was revealed to the public by Yoshiki Okamoto, the president of Capcom's screenplay company Flagship. Resident Evil Zero was designed to be more difficult than its predecessors, removing the item boxes to make the game more like Sweet Home (1989). The real-time "partner zapping" system was designed to take advantage of the console's unique features and strengths, namely the lack of load times, which are necessary for optical disc based gameplay as with the PlayStation. In an effort to make 1-on-1 zombie fights more intense, Capcom experimented with giving the zombies different reactions when they were shot and allowing the player to counter-attack when bitten. The team also toyed with faster zombies, a precursor to Resident Evils crimson head enemies. The prototype also supported local co-operative play. Resident Evil Zero was officially announced at 20 percent completion in January