Photos: Mass shootings 2007-2014

Armed police stand guard near Reynolds High School in response to a school shooting in Troutdale, Oregon.  (Ankur Dholakia / EPA)

Juvenile probation officers Katie Huncovsky and Patrick Kelso pay their respects at a memorial during a community vigil for slain Metro Police officers in front of CiCi’s Pizza in Las Vegas, Nevada June 9, 2014. Police officers Alyn Beck, 41, and Igor Soldo, 31, were ambushed and killed while they were eating lunch in the restaurant by Amanda and Jerad Miller on June 8.   (Steve Marcus / Reuters)

Executive Director of the Injured Police Officers Fund Minddie Lloyd holds a sign with images of the two police officers slain in a shooting June 8, 2014. The Las Vegas Metropolitan Police Department says officers Alyn Beck and Igor Soldo were shot and killed at the restaurant by Jerad Miller and his wife Amanda Miller. Police say the Millers then went into a nearby Wal-Mart where Amanda Miller killed Joseph Wilcox before the Millers were killed by police.  (Ethan Miller / Getty Images)

Two officers were reported shot and killed by two assailants at a pizza restaurant near this Wal-mart on June 8, 2014.  (Ethan Miller / Getty Images)

A policeman secures the scene at Seattle Pacific University after the campus was evacuated due to a shooting that left 1 dead and several wounded.  (David Ryder / Reuters)

The vehicle of the alleged shooter is pictured at one of crime scenes after a series of drive-by shootings in the Isla Vista section of Santa Barbara. Six were killed and seven injured.   (Jonathan Alcorn / Reuters)

A woman kneels in front of a makeshift memorial near the Isla Vista Deli Mart where one of the victims of the deadly shooting rampage was killed May 23, 2014.  (Michael Nelson / EPA)

Blood soaked towels are seen on the floor of an Isla Vista deli, one of the locations of a drive-by mass shooting in Isla Vista, Calif. on May 23, 2014.  (Robyn Beck / AFP/Getty Images)

A soldier pays his respects to the fallen soldiers after President Obama spoke at a memorial service at Fort Hood military base near Killeen, Texas. The memorial service was held for the victims of the shooting that killed three people and wounded 16 more.   (Larry W. Smith / EPA)

A boy touches stockings, representing the 26 elementary school students and school employees killed in the Dec. 14, 2012 shootings at Sandy Hook Elementary School.

Police positioned outside the home of Nancy Lanza on December 18, 2012 in Newtown, Conn. Nancy Lanza was killed by her son before he went on a rampage at Sandy Hook Elementary School on December 14, 2012.  (Don Emmert / AFP/Getty Images)

Sandy Hook Village firefighters observe a moment of silence near Sandy Hook Elementary in Newtown, Conn. on December 21, 2012.

Mourners near the Aurora, Colorado theater where 12 people were killed during a midnight screening of the film, “The Dark Knight Rises.”  (Don Emmert / AFP/Getty Images)

Mourners gather at a roadside memorial across the street from Century 16 theaters in Aurora, Colorado where the mass shootings occurred.   (Mark Boster / Los Angeles Times)

Police surround the apartment of the suspected gunman in the Aurora, Colo. theater killings. Numerous explosive devices were found in the apartment and successfully disarmed.  (Chris Schneider / Getty Images)

Ashleigh Grove grieves over the loss of her friend Micayla Medek during the Century 16 Theater shooting in Aurora, Colorado.  (Joshua Lott / Getty Images)

Students return to Cole Hall almost four years after a deadly shooting in 2008 on the Northern Illinois University campus. A gunman shot and killed five students in a lecture hall and wounded over 20 others.   (Chuck Berman / Chicago Tribune)

Students and DeKalb community members take part in a vigil to mark the second anniversary of the 2008 campus shootings at Northern Illinois University.   (E. Jason Wambsgans / Chicago Tribune)

Eric and Mary Kay Mace, parents of NIU shooting victim Ryanne Mace, stand to remember their daughter after leaving a wreath and flowers at the memorial in front of Cole Hall, the site of the 2008 shootings at Northern Illinois.  (Antonio Perez / Chicago Tribune)

United States Army Soldiers grieve as they pay their respects to their fallen comrades after the Fort Hood Memorial Ceremony held to honor the victims of the shootings.  (Jessica Rinaldi / Reuters)

resident Barack Obama speaks behind the helmets and rifles of the fallen soldiers during the Fort Hood Memorial Ceremony held to honor the 13 victims of the shootings.  (Kevin Lamarque / Reuters)

An injured soldier is wheeled past pictures of slain soldiers and one civilian as they arrive to attend the memorial service at Fort Hood in 2009.  (Kevin Lamarque / Reuters)

Miami Young (L), 11, and Madison Davis, 11, both of Fort Hood, stand at an intersection collecting donations for the troops in Killeen, Texas following the 2009 mass shooting on the base that killed 13.   (Jessica Rinaldi / Reuters)

Virginia State Police make their way to Norris Hall on the Virginia Tech campus in Blacksburg, Va. April 16, 2007. A gunman killed 32 people at the university before killing himself in the deadliest shooting rampage in U.S. history.   (Chris Keane / Reuters)

Savannah Bailey, Bob Bailey, Lynda Bailey and Jacqueline Bales mourn during Virginia Tech’s Day of Remembrance honoring the 32 people killed in the campus shooting rampage.   (Mario Tama / Getty Images)

Mourners gather around a memorial following a remembrance service on the drillfield in front of Burruss Hall on the Virginia Tech campus in Blacksburg, Va., April 23, 2007.  (Michael Tercha / Chicago Tribune)