Those caught up in the excitement and jubilation of last year's Arab spring will be at a loss to reconcile it with the murder of an American ambassador. The brutal killing of Chris Stevens alongside three colleagues in a grenade attack is an unmitigated disaster for those striving to establish democracy in the Middle East and north Africa.

Not only did Stevens die in Benghazi – the cradle of the Libyan revolution – but the diplomat was pivotal in getting the US to support the Nato air attacks that ultimately toppled Colonel Muammar Gaddafi after 42 years. A "clean" intervention was his mantra – facilitating the death of a dictator through superior firepower while not risking a single American life. Now, in a country stripped of a functioning security apparatus and awash with weapons and ammunition, Stevens has met a similarly violent end to Gaddafi.

The perpetrators are not the only ones trying to set their extreme violence in the context of an insult against their Muslim religion. An Egyptian crowd who attacked the US embassy in Cairo on Tuesday was protesting against the same film clips that triggered a storming of the US consulate in Benghazi, and then Stevens' death. All were apparently incensed that the crass images, posted on YouTube, insulted the prophet Mohammed.

The film has nothing to commend it in terms of artistic merit or entertainment value, and it is certainly blasphemous. It portrays the prophet as a sexually incontinent fool, thus evoking the same kind of malevolent caricature which appeared in a Danish newspaper in 2005 and triggered riots across the world, that left at least 50 people dead.

But claiming that Stevens died at the hands of newly democratised Arabs furious at an attack on their faith is disingenuous in the extreme. In fact, it seems certain that Stevens died at the hands of radicals inspired by al-Qaida. Sources in Benghazi – including a factional commander celebrating the death of the ambassador – are already suggesting they were linked to Ansar al-Sharia, a violent Sunni Islamist group that has become notorious for carrying out executions in Libya's second city since the toppling of Gaddafi, as well as attacks on other western interests.

Stevens had worked as a Peace Corps volunteer in north Africa, teaching English in Morocco, and was devoting his professional life to establishing a secure Libya. He was imbued with the spirit of the Arab spring at a time when new Libyan MPs had just taken their seats in parliament, and plans were under way to establish a properly trained police force.

Like the majority of ordinary Libyans, Stevens was powerless to resist a clearly co-ordinated rocket-propelled grenade attack carried out by bandits – ones who are taking advantage of the fledgling nature of their new state to settle scores with the US. Hatred of America did not end when the Arab spring began, any more than the establishment of supposedly tolerant western liberal democracies ended the baiting of Muslims with provocative films and cartoons.

It is no coincidence that Stevens's murder came on the anniversary of the 9/11 terrorist attacks on the US, and after militants were called to avenge the death of Abu Yahya al-Libi, al-Qaida's second-in-command, in north-west Pakistan in June. With the CIA and US military determinedly assassinating figures like Libi and Osama Bin Laden since the start of the "war on terror", so the terrorists' surviving supporters have fought back in kind.

An unstable country such as Libya is an obvious place for such men of violence to rally and prosper. The fact that the Red Cross, as well as aid convoys from the UK, has been attacked numerous times in Benghazi over the past few months gives an indication of the nature of the hateful gangs operating in the area.

There are millions of peaceful, decent Libyans living in the country, but at present it is jihadists who are in the ascendancy. Angry reactions to blasphemous insults are one thing, but the truth is that Libya is currently a hotbed of unregulated, well-equipped and fiercely determined radicals who think nothing of murdering Americans. This is the ultimate message behind the appalling death of Chris Stevens.