In my interview with Father Randall Weber, Exorcist for the Catholic Diocese of Salina, he enumerates the very specific criteria for determining if a person is possessed by a demonic presence. Some of the criteria may surprise you, but it may not surprise you that many suspected incidents of possession fall in to the realm of mental illness. Ultimately, it is the Exorcist, not a Doctor, who must determine if there is a true demonic possession invading a persons spirit.
Father warns against certain activities that might invite the Devil in to your presence, as similarities in how persons have become possessed have been chronicled in writings about exorcism, such as playing with an Ouija Board game. There are other activities as well that you are advised to avoid.
The rite of exorcism does follow a specific ritual of prayer, often said in Latin, and there are significant religious items needed such as a crucifix, holy water and a relic. A relic is a body part of a Saint, or an item closely associated with a Saint. There are grades of relics and, as Father explained, the higher the grade of relic the better to use for an exorcism.
A fascinating piece of the interview was when Father Weber described how you can tell when the demonic spirit has left the person. As he works with a chosen team including two lay persons, this is where I would pray in earnest that the spirit makes a hasty exit and leaves the team in peace. In fact, Father does mention the feeling of peacefulness that acompanies the exiting of the demon.
Although the rite of exorcism is performed by a Catholic Priest, you do not need to be Catholic to seek the services of an Exorcist. This sacramental rite is available to all who seek deliverance from evil. Blessed be Father Weber and his team as they perform this rite in the name of Jesus Christ.
From the Catechism of the Catholic Church~
When the Church asks publicly and authoritatively in the name of Jesus Christ that a person or object be protected against the power of the Evil One and withdrawn from his dominion, it is called exorcism. Jesus performed exorcisms and from him the Church has received the power and office of exorcizing.
The Catholic Rite of Exorcism, the Diocesan Exorcist Speaks
January 28 and 29, 2012
For an Extended Version of the Interview watch the Video