One of the last things you want to hear when you visit the doctor is, it's his or her first day on the job. But a 17-year-old recently managed to give new meaning to the phrase, fake it till you make it. This child scheme had a hospital treating him like a member of the staff. How to get away with and it why they do it. Here's ABC's Matt Gutman. Reporter: Most doctors endure years of school and training before treating patients in a hospital. But for one 17-year-old in west palm beach, Florida, all it took was a white lab coat and a stethoscope. At St. Mary's report the police report says he was walking around the hospital dressed in a white lab coat. I believe it said, department of anesthesiology on it. Reporter: Dr. Sebastian Kent met the 17-year-old last week. They told me he was a doctor. Reporter: Police say unreleased video shows him walking inside the hospital acting like a doctor. Witnesses reported he'd been coming there for a month. But the hospital insists he never treated any patients. In a statement tonight the hospital said, "The individual never had contact with any hospital patients and did not gain access to any patient areas." It insists the safety and security of patients is our highest priority. The day he was arrested at this outpatient building, he was with a relative who actually had an appointment. He introduced himself as this patient's husband. Reporter: He was not a doctor, and she was not his wife. He said, "Oh, Dr. Kent, I really would like to follow you as an intern." I asked him, "Well, you know, what position are you in now?" There the story started to get more vague. Reporter: That's when Dr. Kent figured he was a fraud. His story fell apart. About 30 minutes later he was arrested right here. But this isn't the first time a 17-year-old was busted for channeling his inner do you goy houser. August 2011, Matthew shida, fresh-faced young man, reports for duty in the E.R. Scrubs, stethoscope, a badge identifying him as a P.A., a physician assistant, as close as you can come to being a doctor without an M.D. Do you know if they're hiring here at the hospital? What do you want to do? I'm a doctor. Reporter: Like CHAN in "Catch me if you can," shed oozes office. He's very charming. Reporter: Unlike Leonardo Dicaprio, who gets queasy in the emergency room, shed is drawn to the action. He performed procedures on patients. Reporter: Reporter Nancy Alvarez with channel 9 in Orlando. This kid touched patients. This kid held a child who was getting stitches. He actually administered cpr? Yes, he administered cpr to one patient. Reporter: Apparently unsatisfied, shed demands additional privilege he kept on going back to human resources saying, I need the access. That's when they're like, he's not even a physician assistant or a student. I appreciate you coming down. Reporter: He talks his way from emergency room into a police interrogation room. No, I don't sign off on anything, I just did the circling -- Reporter: Confident he can talk his way out of anything. Sheid waives his right to a lawyer and begins to tell his tale. What do you think it is? And I told him it could be a kidney infection, it could be eti -- He was talking, talking, talking, talking. I have an interest in the medical field. Reporter: An interest, yes. A license, no. In fact, shed had no education, medical or otherwise, beyond a diploma from an online high school. He is not a physician assistant. What he is is a 17-year-old kid with a summer job at a doctor's office. I just did clerical work. I knew one of the physicians. I'm good friends with his daughter. Reporter: He used to run errands to the hospital, so he asked him for an I.D. Badge. And somehow obtained the one that let him prowl the E.R. For a total of nine days. Eventually gaining his medical knowledge from an app. I'd see anatomy and stuff like that, all the anatomy and stuff. Reporter: But the seriousness of his masquerade is soon apparent. One of the teches had to run out of the room to get something and I was told to do it by a physician. Reporter: There's no evidence it was his fault but the elderly patient he did cpr on died the next day. Nancy Alvarez broke the news to the deceased woman's husband. When you told him his wife had been under the care of shed, what did he say? He was shocked. I think he felt pe trayed more than anything. Reporter: Confronted by police, shed blames his charade on the hospital for handing him that incorrect I.D. Badge. What's it even say that I'm a physician's assistant? Let's just say that I was. Are you that stupid that you're just going to put me into the system with that? Without any credentials or any paperwork or nothing? Reporter: The medical center told ABC news, today in our hospital our badging process is significantly more secure." As to why he does these things? Sheid drops hints. Just I felt like I was supposed to be there, I was supposed to be learning, they were supposed to be teaching me. Reporter: The interrogation ends. Sheid is charged and posts bail. Then something inexplicable. He was picked up in Miami, now as an imposter of a police officer? Reporter: Police say shed is packing a badge, a taser, and a loaded pistol. Miami beach cops arrested shed. Pulled up next to a real cop with all the confidence of a real cop, but he's just a kid pretending to be one. Reporter: Back in Orlando, August 2012, he goes on trial for practicing medicine without a license and impersonating a physician assistant. I was sitting just a few feet away from him. And there were tears in his eyes. And he looked petrified. And I felt for him for a moment. And then I wondered, hm. Could this be real? Could he be performing again? We the jury find the defendant guilty of impersonating a physician's assistant --. Reporter: Convicted, he served a year and jail and was released in 2013. He pled guilty to impersonating a police officer. Do you think that the punishment did not fit the crime? People seem to forget this is a 17-year-old child that did these acts. Now you have a 17-year-old kid who made some immature decisions who has had to do time and get a conviction on his record as a felon. He's going to have to deal with that for the rest of his life. Reporter: Whatever the rest of his life holds, he will likely never be a real fi physician, and not a real police officer. Even so, some suspect his career as a professional copycat might not be over. Do you think this is the last time that you will report about Matthew shed? I'm not convinced this is the very last time. The last time we'll see Matthew shed in the news or in our court system. Reporter:? West palm beach the coy hasn't been charged with a crime. He was released to his mother who admits her son wasn't taking his medication and is under the care of a real doctor. I'm Matt Gutman for "Nightline" in west palm beach, Florida.