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By Elizabeth Chuck

The bloodshed at a Louisiana movie theater Thursday night capped an unusually violent week and a half in the United States.

There have been five mass killings in the last 10 days — one of the deadliest stretches in years, according to Jodi Upton, who runs the data journalism team at USA TODAY. The newspaper has tracked mass killings in the United States since 2006.

"I don't think people are aware of just how common mass killings are, that they actually happen every 11 to 12 days," Upton told NBC News. "It's pretty unusual to see five in 10 days."

Behind the Bloodshed: See USATODAY's Data on Mass Killings

The recent spate includes five family members stabbed to death in Oklahoma, three kids and two adults killed in Modesto, California, a woman and her three children found decomposing in their Chicago home, a gunman's attack on a Chattanooga military training center, and four people shot dead in Holly Hill, South Carolina.

The mass shooting at the Lafayette multiplex, which killed three people — including the gunman — and injured nine others, doesn't technically meet the FBI threshold for a mass "killing," defined by four or more dead, excluding the attacker. But the massacre still shares hallmarks of many mass killings:

  • About a third of mass killers don't leave the scene alive, USA TODAY found in its study of more than nine years' worth of data on mass killings.
  • Nearly 1,400 victims have died in 284 mass killings since 2006.
  • Ninety-four percent of suspects in mass killings are male.
  • About 70 percent of mass killings are done by firearms — but not usually the ones committed by women. "There's very few women who commit mass killings. But of those who do, there's a slight tendency to prefer drownings or strangulation or arson," Upton said.

But the theater shooting differed in many ways from general trend lines, too. The average age of male suspects in mass killings is 31; for females, the average age is 33. The Louisiana theater gunman was 59 years old.

RELATED: John Russell Houser Identified as Louisiana Movie Theater Shooter

Public imagination tends to focus on attacks in public places — such as the Aurora, Colorado, movie theater shooting and the Sandy Hook elementary school massacre in Newtown, Connecticut. But less publicized cases make up the majority of the killings.

"Those are very important cases and they're horrific, but more than half of mass killings actually occur among family," Upton said.

Children make up a disproportionate number of the victims, she added: About 30 percent are under the age of 18.

While 57 percent of victims know their killer, there's an element of randomness to many of the slaughters, too.

"Maybe it was a birthday party that someone attended and there was a shooting there. Or you hear a noise at your neighbor's house, and go to see what happened," Upton said.

"It's very easy for us to say, well, I don't do drugs, I don't know any gang members, my family members are stable, I don't worry about that for me. But I do shop at this mall. Or I do go to this movie theater."