The only disservice the movie does is actually telling the extent of what he did and limit really showing how long he got away with murdering patients and how messed up he and his life was. The book was so good and so detailed and I wish the movie was a miniseries instead to go into details.

Cullen started nursing in 1986 but wasn't caught until 2003. He is thought to potentially have started killing as early as his first job. He may have a kill count of over 400 patients. He was shuffled between like 9 different hospitals. Many of which knew he may have or actually harmed or killed a patient but just let him leave instead of doing anything about it.

The movie really only focuses on his last hospital, because Amy played such a vital role in him finally getting caught. But that last hospital dragged their feet, waited months to report the patient death they were legally required to report, and hindered the investigation at all steps to protect themselves. And he killed many patients in that time frame.

Cullen himself was very troubled, had alcohol issues, psych issues, attempted suicide multiple times by swallowing a bottle of pills but then calling 911 or going to the ER himself. Was an animal abuser, stalked a girlfriend, arrested multiple times.