Suppose a group of scientists created a virtual world populated with sentient, self-aware "Sim" people?

Say, hypothetically, a computer scientist created a high-resolution virtual reality world inside a high-power computer, and then, knowing what mechanism causes self-awareness, populated his VR world with a small society of fully sentient self-aware sim-people (like an advanced version of “The Sims” computer game, but not like “The Matrix” because that’s real live people wired into a VR system). Does this scientist have a moral duty to treat these sim people with justice and compassion? Or, since he made them, does the scientist have the right to regard these sim people as his “slaves” to torment and experiment on however he chooses? Bear in mind that, being a “computer simulation” the law has no bearing on what software a scientist writes, and said “sim people” are completely at this scientist’s mercy.