The shooting at an Aurora, Colo., movie theater screening of "The Dark Knight Rises" Friday underscored a chilling trend: While gun violence has plummeted over the decades, mass murder has increased slightly.

Single-victim gun killings have dropped more than 40 percent since 1980, according to 2010 FBI crime data. But the total number of people dying in attacks that claimed four or more victims has climbed from an average of 161 a year in the 1980s to 163 between 2006 and 2008, according to FBI statistics.

Shooting massacres do not mirror the more volatile statistical curve of individual gun violence. Recent incidents -- such as the shooting at a Toronto shopping mall in June -- make it seem as if rampages are on the rise, but they have been a fact of life for a long time and will remain that way, said Jack Levin, a criminology professor at Northeastern University and author of "Extreme Killing."

"They're not decreasing, because the motive in mass murder is so different from the motivation for single-victim murders," Levin told The Huffington Post. "These are well-planned crimes ... Mass killings don't depend on any given time."

Most mass murderers seek revenge of some sort, Levin said. In contrast, individual killings are mostly sparked by flared tempers, such as an argument in a bar where someone suddenly pulls a gun, Levin said. The frequency of one-on-one gun encounters is far more susceptible to changes in social climate and law enforcement, he added.

One-on-one violence also usually involves a small-caliber handgun while mass killers often opt for an semi-automatic weapons to kill as many as possible, Levin said. The amount of lives lost seizes our attention, magnifying their impact.

Between 1980 and 2008, 4,685 people died in 965 mass-murders, a Scripps-Howard study of FBI data revealed. Despite recent headline-grabbing incidents -- such as Binghamton in 2009 and the Tucson shooting in 2011 that nearly killed for Rep. Gabrielle Giffords -- group murders have remained close to the average of 20 a year for decades, according to USA Today.

Although a 19-year-high 47 percent of American adults report owning a gun, the firearm homicide rate has dipped remarkably. Gun murders sank from more than 10,000 in 2005 to 8,776 in 2010, and appeared to drop again in 2011, according to a recent FBI preliminary report.

Gary LaFree, a criminology professor at the University of Maryland, told msnbc.com that the crime rate is at its lowest since World War II.

But to Levin, the prospect of mass murder will remain frighteningly steady. "I don't think there's very much we can do about it," he said.

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  • Tom Sullivan , holds a photograph of his son, Alex Sullivan, as he pleads with the media to help him find his son, outside Gateway High School on Friday, July 20, 2012 in Aurora, Colo. Alex Sullivan, was celebrating his 27th birthday by attending midnight premiere of the Batman movie Friday night. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • A woman cries outside Gateway High School where witness were brought for questioning after a gunman opened fire at a midnight premiere of The Dark Knight Rises Batman movie Friday, July 20, 2012 in Aurora, Colo. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • Tom Sullivan, center, embraces family members outside Gateway High School where he has been searching frantically for his son Alex Sullivan who celebrated his 27th birthday by going to see "The Dark Knight Rises," movie where a gunman opened fire Friday, July 20, 2012, in Aurora, Colo. (Photo credit: AP Photo/Barry Gutierrez)

  • Eyewitness Chandler Brannon, 25, sits outside Gateway High School where witnesses were brought for questioning after a shooting at a movie theater showing the Batman movie "The Dark Knight Rises," Friday, July 20, 2012 in Aurora. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • A small group prays outside Gateway High School where witness were brought for questioning Friday, July 20, 2012 in Aurora, Colo. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • Family and friends wait outside Gateway High School where witnesses were brought for questioning after a shooting at a movie theater showing the Batman movie "The Dark Knight Rises," Friday, July 20, 2012 in Aurora, Colo. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • Eyewitness Jacob Stevens, 18, hugs his mother Tammi Stevens after being interview by police outside Gateway High School where witnesses were brought for questioning Friday, July 20, 2012 in Aurora, Colo. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • Eyewitness Isaiah Bow hugs his mother Shamecca Davis after being questioned by police outside Gateway High School where witnesses were brought in, Friday, July 20, 2012 in Aurora, Colo. After leaving the theater Bow went back in to find his girlfriend. "I didn't want to leave her in there. But she's ok now," Bow said. A gunman wearing a gas mask set off an unknown gas and fired into the crowded movie theater killing 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • Emma Goos, 19, hugs her mother, Judy Goos, outside Gateway High School where witnesses were brought for questioning Friday, July 20, 2012, in Aurora, Colo. Emma was in the third row of the theater of the new Batman movie when the shooter entered. She helped apply pressure to a man's head who was injured. (Photo credit: AP Photo/Barry Gutierrez)

  • Police cars in front of the Century 16 theater in Aurora, Colorado where a gunman opened fire during the opening of the new Batman movie "The Dark Knight Rises" killing at least 15 people and wounding 50 others on the morning of July 20, 2012. The shooting suspect in custody after at least 12 people were shot dead and around 50 were wounded at a movie screening in the United States has been identified as 24-year-old James Holmes, US media said Friday. Television networks cited the FBI as saying that Holmes, from the town of Aurora, Colorado, scene of the midnight shooting at a screening of the Batman movie "The Dark Knight Rises," did not appear to have any known terrorism connections. (Photo credit: AFP PHOTO/JONATHAN CASTNER JONATHAN CASTNER/AFP/GettyImages)

  • Police tape cordons off the parking area around the Century 16 movie theater in Aurora, Colorado, July 20, 2012 where a gunman opened fire during the showing of the new Batman movie. At least 12 people were killed and around 50 wounded in the cinema shooting. (Photo credit: AFP PHOTO JONATHAN CASTNERJONATHAN CASTNER/AFP/GettyImages)

  • Police cars in front of the Century 16 theater in Aurora, Colorado where a gunman opened fire during the opening of the new Batman movie "The Dark Knight Rises" killing at least 15 people and wounding 50 others on the morning of July 20, 2012. The shooting suspect in custody after at least 12 people were shot dead and around 40 were wounded at a movie screening in the United States has been identified as 24-year-old James Holmes, US media said Friday. Television networks cited the FBI as saying that Holmes, from the town of Aurora, Colorado, scene of the midnight shooting at a screening of the Batman movie "The Dark Knight Rises," did not appear to have any known terrorism connections. (Photo credit: AFP PHOTO/JONATHAN CASTNERJONATHAN CASTNER/AFP/GettyImages)

  • Police cars in front of the Century 16 theater in Aurora, Colorado where a gunman opened fire during the opening of the new Batman movie "The Dark Knight Rises" killing at least 15 people and wounding 50 others on the morning of July 20, 2012. The shooting suspect in custody after at least 12 people were shot dead and around 50 were wounded at a movie screening in the United States has been identified as 24-year-old James Holmes, US media said Friday. Television networks cited the FBI as saying that Holmes, from the town of Aurora, Colorado, scene of the midnight shooting at a screening of the Batman movie "The Dark Knight Rises," did not appear to have any known terrorism connections. (Photo credit: AFP PHOTO/JONATHAN CASTNERJONATHAN CASTNER/AFP/GettyImages)

  • Police cars are seen in the parking area around the Century 16 movie theater in Aurora, Colorado, July 20, 2012 where a gunman opened fire during the showing of the new Batman movie. At least 12 people were killed and around 50 wounded in the cinema shooting. (Photo credit: AFP PHOTO JONATHAN CASTNERJONATHAN CASTNER/AFP/GettyImages)

  • Police use a video camera to look inside an apartment where the suspect in a shooting at a movie theatre lived in Aurora, Colo., Friday, July 20, 2012. As many as 12 people were killed and 50 injured at a shooting at the Century 16 movie theatre early Friday during the showing of the latest Batman movie. (Photo credit: AP Photo/Ed Andrieski)

  • Police break out a window of an apartment where the suspect in a shooting at a movie theatre lived in Aurora, Colo., Friday, July 20, 2012. As many as 12 people were killed and 50 injured at a shooting at the Century 16 movie theatre early Friday during the showing of the latest Batman movie. (Photo credit: AP Photo/Ed Andrieski)

  • Shamecca Davis hugs her son Isaiah Bow, who was an eye witness to the shooting, outside Gateway High School where witness were brought for questioning Friday, July 20, 2012 in Denver. After leaving the theater Bow went back in to find his girlfriend. " I didn't want to leave her in there. But she's ok now," Bow said. A gunman wearing a gas mask set off an unknown gas and fired into a crowded movie theater at a midnight opening of the Batman movie "The Dark Knight Rises," killing at least 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • Judy Goos, second from left, hugs her daughters friend, Isaiah Bow, 20, while eye witnesses Emma Goos, 19, left, and Terrell Wallin, 20, right, gather outside Gateway High School where witness were brought for questioning Friday, July 20, 2012 in Denver. A gunman wearing a gas mask set off an unknown gas and fired into a crowded movie theater at a midnight opening of the Batman movie "The Dark Knight Rises," killing at least 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

  • A SWAT team officer stands watch near an apartment house where the suspect in a shooting at a movie theatre lived in Aurora, Colo., Friday, July 20, 2012. As many as 14 people were killed and 50 injured at a shooting at the Century 16 movie theatre early Friday during the showing of the latest Batman movie. (Photo credit: AP Photo/Ed Andrieski)

  • Police gather near an apartment house where the suspect in a shooting at a movie theatre lived in Aurora, Colo., Friday, July 20, 2012. As many as 12 people were killed and 50 injured at a shooting at the Century 16 movie theatre early Friday during the showing of the latest Batman movie. (Photo credit: AP Photo/Ed Andrieski)

  • A SWAT team officer stands watch near an apartment house where the suspect in a shooting at a movie theatre lived in Aurora, Colo., Friday, July 20, 2012. As many as 12 people were killed and 50 injured at a shooting at the Century 16 movie theatre early Friday during the showing of the latest Batman movie. (Photo credit: AP Photo/Ed Andrieski)

  • Jacob Stevens, 18, hugs his mother Tammi Stevens after being interview by police outside Gateway High School where witness were brought for questioning after a shooting at a movie theater, Friday, July 20, 2012 in Denver. A gunman wearing a gas mask set off an unknown gas and fired into a crowded movie theater at a midnight opening of the Batman movie "The Dark Knight Rises," killing at least 12 people and injuring at least 50 others, authorities said. (Photo credit: AP Photo/Barry Gutierrez)

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  • Police are pictured outside of a Century 16 movie theatre where as many as 12 people were killed and many injured at a shooting during the showing of a movie at the in Aurora, Colo., Friday, July 20, 2012. (Photo credit: AP Photo/Ed Andrieski)

  • Police are pictured outside of a Century 16 movie theatre where as many as 12 people were killed and many injured at a shooting during the showing of a movie at the in Aurora, Colo., Friday, July 20, 2012. (Photo credit: AP Photo/Ed Andrieski)

  • Aurora Police Chief Daniel Oates talks to media at Aurora Mall where as many as 12 people were killed and many injured at a shooting at the Century 16 movie theatre in Aurora, Colo., Friday, July 20, 2012. (Photo credit: AP Photo/Ed Andrieski)

  • Aurora Police Chief Daniel Oates talks to media at the Aurora Mall where as many as 14 people were killed and many injured at a shooting at the Century 16 movie theatre in Aurora, Colo., Friday, July 20, 2012. (Photo credit: AP Photo/Ed Andrieski)

  • Police are pictured outside of a Century 16 movie theatre where as many as 12 people were killed and many injured at a shooting during the showing of a movie at the in Aurora, Colo., Friday, July 20, 2012. (Photo credit: AP Photo/Ed Andrieski)

  • Police are pictured outside of a Century 16 movie theatre where as many as 12 people were killed and many injured at a shooting during the showing of a movie at the in Aurora, Colo., Friday, July 20, 2012. (Photo credit: AP Photo/Ed Andrieski)

  • People gather outside the Century 16 movie theatre in Aurora, Colo., at the scene of a mass shooting early Friday morning, July 20, 2012. Police Chief Dan Oates says 12 people are dead following the shooting at the suburban Denver movie theater. He says 50 others were injured when gunfire erupted early Friday at the Aurora theater. Oates says a gunman appeared at the front of one of the Century 16 theaters. <em>Photo Credit: Karl Gehring, <a href="http://www.huffingtonpost.com/news/exposure/" target="_hplink">Denver Post</a>. </em> / AP

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