WATCH: Police Find 13 Page Confession of Nurse Who Murdered Patients

Nurse Victorino Chua has been found guilty of murdering two people and poisoning dozens of patients where he worked.

The father-of-two injected insulin into saline solutions and returned them to storage so unknowing colleagues would used the poison on patients. He also falsified information on patients’ charts to increase the dosage of prescribed drugs.

In 2011, two years after Chua began working at Stepping Hill hospital in Stockport, England, patients began to suffer from attacks of low blood sugar levels (from the insulin he injected into their remedies). Two patients—one 44 years old, the other 83—died. A 41-year-old Grant Misell has been told he might never recover from the serious brain damage he suffered at Chua’s hands.

After his arrest, police found Chua’s self-titled “Bitter Nurse Confession,” a 13-page document in which he admitted there’s “a devil” inside him. In the letter Chua says, in broken English: “I’m writing this letter in case something happen to me my family can continue my case or can tell somebody to look at it and work out how an angel turn to an evil person. Inside of me I can feel the anger that any time it will explode. Just still hanging on can still control it but if I will be pushed they gonna be sorry.

Chua was seeking help for his anger and frustration with visits to an occupational health counselor at his work, where he took care of some of the most vulnerable members of society, often people in their 70s and 80s, who had come to the hospital to die.

The daughter of one of Chua’s victims has a hard time understanding why a nurse murders patients and so indiscriminately: “The fact that it happened to our mum is extremely distressing and heartbreaking. Because it’s so apparently random as well. Why her?” Her mother Linda McDonagh was a 59-year-old with motor neurone disease. She was unable to tell nurses how she felt once the insulin took hold. She died seven months later.

According to detective Barraclaugh, “[Chua’s] certainly not mentally ill. Whenever he’s challenged, whether it be by the hospital, patients or relatives looking after those patients, or whether it be by fellow members of staff, that’s what sends him into a rage. I think there is an element of arrogance there. I think there’s an element of control. He really, really did not like being challenged.”