Answer: Dr. Briggs
Dr. Briggs was the prosecution's second expert to testify about Emily's medical condition. He was the one who came up with this notion of psychotic epileptic disorder. Dr. Cartwright was the anonymous doctor who Father Moore called in to oversee Emily's physical condition. He did not reveal the doctor's identity, but Cartwright came forward with the audio tape of the exorcism, and wanted to testify on Father Moore's behalf. Unfortunately he was killed, right in front of Erin Bruner, before his court appearance.
Emily had received a vision of the virgin mother after the exorcism. The holy spirit had offered her the chance to abandon her demonically wracked body and be free from pain. But, if she stayed inside her body she'd reveal the demonic powers to thousands of people. Emily chose to stay in her body, and received the stigmata after returning. The stigmata was argued away as Emily gripping her barbed wire fence after the "vision" had occurred.
Father Moore was found guilty of negligent homicide, but the jury recommended him to a sentence of time served. The judge agreed and Father Moore was released.