It seems like there’s a lot of activity going on in New York right now. The individual who observed this excorism is
Richard E. Gallagher, M.D., is a board-certified psychiatrist in private practice in Hawthorne, New York, and Associate Professor of Clinical Psychiatry at New York Medical College. He is also on the faculties of the Columbia University Psychoanalytic Institute and a Roman Catholic seminary. He is a Phi Beta Kappa graduate of Princeton University, magna cum laude in Classics, and trained in Psychiatry at the Yale University School of Medicine.
The New Oxford Review has the full article of the case. While there may be natural explanations for this as a believer I know demons exist.
With a team of priests, deacons, several lay assistants, psychiatrists, nuns, some of whom also had medical and psychiatric training,
However, it would be difficult to disprove. In the end either one believes that there are malevolent forces or not and no evidence one way or the other will likely change ones view.