Not only did he stop seeing Fenton, he also stopped taking sertraline. We can’t be sure exactly when he stopped but his final prescription would have run out around 26 June. The shootings were on 20 July. For some experts who believe sertraline may have played a role in reducing Holmes’s fear of consequences and even prompted delusional thinking, this gap in the timeline prevents them from blaming the drug for what happened.

The fact that Mr Holmes was off it for three weeks even though he had the abrupt ending, means to me that it was unlikely, or I can’t say impossible, but played a very small role rather than a major role.” Philip Resnick

The Royal College of Psychiatrists says: “Up to a third of people who stop SSRIs have withdrawal symptoms which can last between two weeks and two months… for a small number of people they can be quite severe.” Prof Peter Tyrer, a UK-based expert on personality disorders who has been involved in evaluating the effectiveness of SSRI antidepressants since they first came on the market three decades ago, says stopping them suddenly is very unwise.

Prof Peter Tyrer

“It’s well established that you have a withdrawal problem and these adverse effects that you may have had even when starting the drugs. They all come back with a vengeance and if you’re still having them when you stop the drugs they come back even more strongly.” He adds: “It can be six or seven weeks before the effects wear off, and in some cases – and this is one of the problems with these drugs – sometimes they last even longer than that.” After stopping the drugs, Holmes started doing things he’d never done before. He dyed his hair red, created a profile on a swingers’ sex website, and started to draw detailed plans of the shootings in his notebook.

Holmes's internet dating profile photo

Holmes also visited the cinema in Aurora, and by the beginning of July went to a shooting range in the Rocky Mountains. There he began practising with the weapons he’d bought. On 8 July, classmate Hillary Allen got some odd texts from him. “The floodgates are open... It’s in your best interests to avoid me, am bad news bears,” Holmes wrote. “The next time I actually heard about James at all was when the shooting happened,” says Allen.

Holmes brandishing a gun and wearing dark contact lenses

I was in complete disbelief that it was actually James. Then immediately my mind goes back to those messages and thinking like, ‘Oh my gosh,’ like this was real, like he was actually like really, really struggling with something.”

What Holmes was struggling with – mental illness, the side effects of his legally prescribed medication or a combination of the two – we may never know for sure. I’ve found no evidence Holmes planned to kill before he took antidepressants and plenty afterwards to suggest his mental state went rapidly downhill. Peter Tyrer says: “His symptoms were exactly right for giving sertraline... but with his underlying personality, with that sort of person... some of the underlying predispositions can come out more strongly, and in the case of Holmes these were very dangerous indeed.” In a statement Pfizer, the company that developed sertraline, said: “Based on currently available scientific evidence, a causal link between the use of sertraline and homicidal behaviour has not been established. Sertraline has helped millions of patients diagnosed with major depression and anxiety disorders, including Obsessive Compulsive Disorder and Post-Traumatic Stress Disorder.”