Fringe Episode 2.11 Unearthed

When a young girl, Lisa, is pronounced dead, the doctors begin the process of harvesting her organs until she suddenly wakes up on the operating table spewing out a series of numbers. The Fringe team is called in to figure out how she was revived and what those numbers meant. In addition to her rising from the dead, she also has a new-found ability to speak Russian and possesses classified information only a high-ranking soldier would know. The team comes to realize that a soldier named Rusk was murdered at the same exact time that the girl has died, thus determining that the girl is possessed by that man. The team discovers that this man is on a mission to revenge his wife who had him killed.

Walter posits that, due to a heavy radiation exposure, Rusk's energy wasn't completely dispended. He is thus able to possess Lisa at time of death. Rusk possessed Lisa long enough to deal with unfinished business with his wife and until Lisa is eventually able to purge him from her consciousness.