Paul Thomas: Gunman on a rampage? We've heard it all before

They're coming so thick and fast that it's hard to differentiate. You really have to focus on the specifics to tell them apart because the basic storyline - gunman on killing spree - is always the same.

And repetition breeds numbness. It's getting to the stage where you almost have to force yourself to be appalled.

On March 10, a fortnight after quitting his job at the local sausage factory, "quiet but well-liked" Michael McLendon shot his mother, grandparents, aunt and uncle, two cousins and four other people, including an 18-month-old girl, who happened to be in the wrong place at the wrong time. He also shot the family dogs. That was in Alabama.

Three weeks later in Santa Clara, California, a "bright, quiet" engineer at Yahoo named Devan Kalathat killed his brother-in-law and sister-in-law, their daughter, and his own son and daughter.

The following day, "good old country farm guy" Robert Stewart gunned down seven patients and a nurse at a nursing home in North Carolina.

Last weekend there was a triple-header. Jiverly Voong, about whom no one seemed to have a positive word to say, killed 13 people at an immigration centre in Binghamton, New York.

In Pittsburgh, Pennsylvania, Richard Poplawski shot dead three police officers who'd responded to a domestic disturbance call from his mother. She and her son had had a row over a dog urinating in the house.

And up in the Pacific northwest, James Harrison, described as a strict, controlling husband and father, shot his five children.

The most obvious common factor is family conflict. McLendon was embroiled in a legal dispute with members of his family; Kalathat had an argument with his brother-in-law who'd recently arrived from India; Stewart went to the nursing home looking for his estranged wife who worked there; Harrison had discovered his wife was leaving him for another man and would've killed her too if she'd been where he thought she was.

With the possible exception of Kalathat, none of the killers had impressive CVs or bright prospects: McLendon failed police academy; Poplawski was rejected by the Marines; Voong had recently lost his job; Harrison impregnated his wife-to-be when she was 13.

But only Voong ticked enough boxes to qualify as a ticking time-bomb - his wife and kids had left him; he was obsessed with guns; he seethed with self-pity and resentment; he talked about wanting to kill the President.

Besides, many people get put through the wringer of relationship breakdown, family conflict and unfulfilled ambition without going on killing sprees. Women, who suffer more than their fair share of life's disappointments, virtually never do.

Four of the killers committed suicide. The two who did not hadn't slain a family member.

They were all over-equipped with firearms designed primarily if not specifically for killing human beings.

This isn't a uniquely American phenomenon. Last month a teenager killed 15 students and teachers at a school in a Stuttgart suburb, the second such rampage in Germany in the space of seven years. Finland, of all places, has had two high school massacres in the past 18 months.

And while the media and Hollywood can give the impression not much has changed in the US since the Earp brothers and the Clanton gang faced off, statistics suggest otherwise.

The overall US crime rate is not significantly different to a number of Western countries; for some offences it's actually lower. The US murder rate has halved over the past two decades and is now back to where it was in the mid-1960s.

Roughly 8000 fewer people a year are being murdered than in the early 1990s, even though the population has increased by around 45 million.

But while the US murder rate has fallen, it's still significantly higher than other Western countries. And when the focus is narrowed to murders involving firearms the discrepancy is marked: America has 7.5 times as many gun murders as the next worst Western country.

But, as Barack Obama said during the election campaign, Americans cling to their guns. Until Poplawski began killing police officers in cold blood, he could have been a poster boy for the gun lobby with his ill-informed muttering about the new Administration's plans to infringe his constitutional right to bear arms.

We can only wonder what perceived threat prompted him to acquire a bullet-proof vest, military assault rifle and several handguns and become the enemy within. We can only wonder how many more like him are out there.