Manchester bomber Salman Abedi

What was going through Salman Abedi’s mind when he made that journey to Manchester Arena on Monday night? How does someone do something so unspeakably evil as to slaughter and grievously injure innocent young children in this way?

Was he a psychopath? Was he evil? I do not know the answer but I do know, as the Mail reports today, that according to his friends Abedi was a frequent and heavy cannabis smoker.

Religious belief tends to be associated with lower rates of alcohol and drug use, but cannabis has been shown to increase people’s preoccupation with religion, especially in young men.

Surely, it is no coincidence that time and time again, in the aftermath of recent terrorist attacks, as we learn more about the perpetrators and try to understand their motivation, we discover that cannabis was a part of their daily lives.

Mohammed Emwazi, known as Jihadi John — the man who murdered hostages James Foley, Alan Henning and David Haines, among others — was reportedly a heavy cannabis smoker.

Richard Reid, the shoe bomber who tried to blow up a plane flying from Paris to Miami in 2001, smoked cannabis as a youngster, as did the killers of Fusilier Lee Rigby, Michael Adebolajo and Michael Adebowale.

London Tube knifeman Muhaydin Mire, left, and San Bernardino massacre perpetrator Tashfeen Malik, right

French train terrorist Ayoub El Khazzani, left, and Charlie Hebdo killer Said Kouachi, right

Amal el-Wahabi, one of the first British women to be convicted of terror offences — she was raising funds for her husband who was fighting for ISIS — since the Syrian conflict began, smoked the drug, as did Paris bomber Ibrahim Abdeslam.

Aine Davis, the British jihadi convicted in Turkey on terrorist offences earlier this year, was a former drug dealer and cannabis addict. Police raids on the apartments of those involved in the terrorist atrocity in Paris in 2015, found they were littered with joints and other evidence of the drug’s use.

Orlando club killer Omar Mateen, left, and Tunisia beach gunman Seifeddine Rezgui, right

Tunis beach killer Seifeddine Rezgui; the Belgian train terrorist Ayoub El-Khazzani; the Leytonstone knife attacker Muhaydin Mire; Khalid Masood, who carried out the Westminster attack in March; ringleader of the 7/7 London bombings, Mohammad Sidique Khan . . . I could go on.

It is a roll call of horror that should shame the liberal elite who push for a loosening of drug laws. It is their complacency and ignorance that has led to the epidemic of cannabis use that clinicians like me encounter on a daily basis and are powerless to stop.

I’ve seen so many lives wrecked by the drug — but they are the tip of the iceberg. The collateral damage is equally as devastating.The evidence for the dangerous effect of cannabis could not be clearer. The link between the drug and psychosis is well established.

Isis monster 'Jihadi John', left, and Germany bomber Mohammad Daleet, right

While the pro-cannabis lobby does its best to minimise the evidence for effects on mental health, The Royal College of Psychiatrists backs current research showing that regular use has been found to double the risk of a psychotic episode or of developing schizophrenia.

All too frequently, courts hear how individuals have become psychotic after smoking the drug and, in the grips of paranoia and delusions, have committed murder in cold blood.

It is impossible to know if Salman Abedi was psychotic when he blew himself and his victims up. But there is emerging evidence that cannabis does far more than elevate the risk of psychosis.

The drug also has a profound and serious impact on the user’s psychology, affecting the way they behave and think and, most chillingly, view others.

We know cannabis can make people feel apathetic and withdrawn and that these effects can last for years, even if they have stopped using. However, developments in brain scanning techniques show the drug’s impact on specific parts of the brain, and it is this that is ringing alarm bells.

Jailed Isis member Aine Davis, left, and Nice atrocity perpetrator Mohamed Lahouaiej, right

Research by Texas University in 2014 found cannabis causes the orbitofrontal cortex to shrink, the area of the brain involved in mental processing and decision-making. It also plays a crucial role in empathy. Shrinkage can have a devastating effect, stunting someone’s ability to engage with the emotional responses of others. They become more callous.

Without the ability to empathise, not only is it easier to disregard the welfare of others, but also to understand the consequence of their actions. It deadens people to the impact of their behaviour.

Cannabis has also been shown to make people more suggestible and compliant — making users vulnerable to those looking for young, weak, pliable minds to brainwash. And there is evidence suggesting the damage to the brain is long lasting. Of course, I am not suggesting cannabis use can turn someone into a suicide bomber or terrorist.

Nor am I suggesting that using cannabis absolves people of responsibility. But I believe we can’t ignore the common thread running through the history of many of these extremists who have brought death and mayhem to cities around the world.

Lee Rigby killers: Michael Adebolajo, left, and right Michael Adebowale

Given what we know about the effects of cannabis, is it possible that the drug makes some users more susceptible to the warped, twisted ideology of hate that the Islamists promote by stripping the users of their usual empathy?

Studies into the personality type of would-be jihadi terrorists have found some recurring themes that make an individual ‘ripe’ for radicalisation. They tend to feel angry, alienated or disenfranchised.

There is also a strong sense of victimhood and that they are fighting for a social injustice.

They have a poor sense of identity and tend to be ‘adolescent’ and petulant. This kind of personality type, combined with cannabis use, surely produces an individual more receptive to the kind of hate-filled rhetoric peddled by radical Islamists.

For too long, we have ignored the terrible toll of this drug. Too many people have dismissed cannabis as harmless — something to help you relax and chill — and that an individual should be free to buy and use as they choose.

Now, more than ever, we need to wake up to a pernicious substance that ruins not just the lives of those that take it, but countless others around them in ways we might never have imagined.