McKinley Psychiatric Hospital is the psychiatric facility where Zack Addy was Institutionalized. He was sent there for his role in the rampage of another Serial Killer; Gormogon. The Head of the psychiatric hospital was Dr. Mihir Roshan, another Serial Murderer known as The Puppeteer. After he was exonerated for the murder of Ray Porter, Zack still has to serve out the last thirteen months of his sentence at the institution before he can be released, since the charge for aiding Gormogon during his crime spree still stands, which he accepts, stating that the last thirteen months are nothing compared to what he has been through for the past eight years.
When Zack confessed to the murder of Ray Porter in The Pain in the Heart, he made a deal with Caroline Julian to be legally declared non compos mentis, so he could be sent to a secure psychiatric facility instead of going to prison if he co-operated with her completely.
The institution made its first appearance in The Perfect Pieces in the Purple Pond when Sweets was having a conversation with Zack about his "delusions" when he was working for Gormogon. Zack merely stated that he was wrong, not delusional. Sometime during their conversation, Zack swapped the magnetic strip on his "loony bin library card" with the magnetic strip on Sweets' key card in order to escape and help Booth and Brennan solve the murder of Jared Addison. After solving the crime and having a conversation and possibly a meal with his friends at the Royal Diner, he willfully returned to the institution with Booth. Outside the institution when Booth left, Zack confessed to Sweets that he never actually killed Ray Porter, but he only told Gormogon where to find him. He believed that he would have killed him if Gormogon asked, but Sweets told him that nobody has any idea if they are capable of ending a life until they are put in that situation and Sweets realized at that moment that Zack, at heart, is not a killer. Sweets wanted to tell Brennan and Booth the truth, but Zack forbade him since he is his patient and that he is ethically not allowed. Zack feared that since he is still an accessory to murder, if his secret were to come out then Booth would take him out of the institution and throw him into prison and Hodgins assured him that he would not do well in prison. Sweets wanted him to tell the truth because he believed that The Apprentice is still out there, but Zack told Sweets that Gormogon killed him so he could recruit Zack since "there could only ever be two." Zack reminded Sweets that unless he gives him permission to do so, if Sweets told anyone the truth about the murder of Ray Porter then he would be violating their doctor-patient confidentiality. The episode closes with Zack at the institution and Sweets keeping Zack's secret, despite his worries about Zack.
In The Nightmare within the Nightmare, Booth barged into McKinley Psychiatric Hospital to find Zack because he believed that Zack was the most recent Serial Murderer; The Puppeteer, but when he got to his room, he only found a pile of books under his sheets. The episode ends with Brennan meeting Zack in an unknown location which was eventually revealed to be The Gormogon Vault within the basement of the Jeffersonian Institution.
In The Hope in the Horror, Zack was proclaiming his innocence for the murders and was willing to co-operate to prove it, even going as far as attempting to inject himself with Sodium Thiopental; truth serum to convince Brennan. Dr. Mihir Roshan, the Head of McKinley Psychiatric Hospital, told them about how Sweets was visiting Zack almost every week for the past seven years before he died. When Sweets was murdered Zack had trouble processing and he fell into a fit of rage which caused him to self-injure which left a long scar across his head. Ever since then, Zack has been different, withdrawn. Zack told Aubrey about how he has been allowing himself free time at night outside the sanitarium and breaking into the local library to read and catch up with his friends' lives by hacking into their E-mail accounts. Angela was able to prove that Zack was hacking into their E-mail accounts, although he did show some sense of discretion by avoiding all the photo attachments. Angela discovered that Zack was consulting with Hodgins' physical therapist under another name; Dr. Alexander Bancroft. Zack was helping Hodgins recover from being paralyzed with a procedure developed by the real Dr. Alexander Bancroft; who is a world-renowned neurosurgeon. Karen Delfs wanted to give Zack access to the case file in case Zack can find something the team missed. She discovered that The Puppeteer suffers from D.I.D. (Dissociative Identity Disorder). Although Zack doesn't display any symptoms, Karen believed that it could have been brought on by the trauma to his head. She believed that if she confronts him with what he did, then the other personality will present itself. Zack and Brennan were able to look through all the evidence they have on The Puppeteer in the FBI Interrogation Room. Zack told Dr. Roshan that he wants to return to the institution, only this time to Maximum Security. Brennan and Zack agree that the circumstantial evidence against Zack is conclusive.
After Booth dropped Zack off at McKinley Psychiatric Hospital, Brennan called Booth after she discovered that the identity of The Puppeteer was Dr. Roshan and Booth hurried back to get to Zack. As Dr. Roshan was ready to inject him with Succinylcholine, Zack recognized that it was the same poison that was used to kill the other three victims after looking at the injection vial and attacked him. Zack was able to temporarily disorient Roshan and had a chance to kill him, but ultimately couldn't do it. Dr. Roshan stabbed Zack's leg with his pen and was about to finish him off, but Booth barged into the room and shot Roshan in the back of the spine, killing him and saving Zack. The next day, Booth and Brennan visited Zack at the garden outside the sanitarium and offered to have him transferred to another psychiatric facility given everything that has happened. Zack agreed that the time has come to leave McKinley Psychiatric Hospital and re-enter society. Zack told Booth and Brennan that he never murdered Ray Porter and that he confessed because he assumed that he would if Gormogon told him to until he learned that he is not capable of killing, not even to save himself. Brennan agreed to re-examine the evidence and Booth agreed to help him get released.
In The Day in the Life, the evidence gathered from the body of the Apprentice is enough to exonerate Zack of the murder charge and life sentence at his appeal. However, the judge determines that he is still guilty of the crime of aiding a known killer and orders that Zack finish out the last thirteen months of his sentence for that crime. While not outright stated, Zack presumably finishes out his sentence at McKinley.