Can ghosts be found within the Christian religion?
No Ghosts in Most Christian Denominations
Christianity, especially Christian Fundamentalists, argue against the existence of ghosts due to their teaching of an eternal hell. Fundamentalists believe that people cannot become ghosts, as upon death, people will either find themselves in an eternal state of bliss they call "Heaven" or in an eternal place of suffering they call "Hell." Therefore, there is no place left for a ghost to exist, in this and similar Christian doctrines, as teachers from these religious groups will not recognize any biblical passages stating to the contrary. Interestingly, Judaism gave rise to Christianity, but in contrast, teaches the existence of ghosts and ghost possession. And passages that are in the Hebrew Bible (the same as the Christian Bible's Old Testament) do tell of ghosts (e.g. King Saul being vexed by a ghost, known as a dybbuk).
Ghosts Within Catholicism
Catholicism, the forerunner to most of today's varied Christian sects and denominations does allow for the existence of ghosts, when one considers that Catholic doctrines teach of a place that exists between Heaven and Hell called "purgatory." Purgatory is believed to be a place for souls who die in a state of grace to go through temporary punishment as a cleansing process, eventually preparing them for Heaven. This idea of a cleansing process is paralleled somewhat by the teachings of Judaism, and an offshoot of Catholicism: Mormonism. Both religions teach the eventual redemption of all of mankind.
The Catholic idea of purgatory has been described often as a place of intense, painful fire, though it better metaphorically symbolizes the inner cleansing of a person, as going through a refiner's fire. Roman Catholics believe the fate of a person in purgatory can be affected by the actions of those on earth. Perhaps, purgatory's cleansing process is similar to how ghosts suffer, remaining earthbound, interacting with the living, and in a state of trauma until they can move on unto peace and continue their life journey. Just maybe, purgatory, a place of suffering, is found here on Earth.