The Thirteenth Floor
Computer scientist - billionaire Hannon Fuller discovers something extremely important. Learning that he's targeted for assassination, he leaves a message in the virtual reality world he's designed (which appears to be Los Angeles in 1937 with seemingly real people and real materials) to his colleague Douglas Hall, hoping he can discover it. Bakc to the real world, Fuller is murdered at the same night, with Hall being the number one suspected and indeed finds a bloody shirt in his house, with no memory of what happened the night before. Hall then embarks in Fuller's mysterious created world to try to find out the culprit, and what's waiting for him ahead is rougher than he could ever expect.