An attack at a Southern California social services center Wednesday became the latest mass shooting in the United States.

Here's a look at some of the deadliest U.S. shootings since 2012:

— Dec. 2, 2015: As many as three gunmen believed to be wearing military-style gear opened fire at a social services center in San Bernardino, California, killing at least 14 people and wounding more than a dozen, authorities said. No one has been arrested in the shooting, and a motive is unknown.

— Oct 1, 2015: A shooting at Umpqua Community College in Roseburg, Oregon, left 10 people dead and seven wounded, authorities said. Shooter Christopher Harper-Mercer, 26, exchanged gunfire with police then killed himself.

— June 17, 2015: Dylan Roof, 21, shot and killed nine African-American church members during a Bible study group inside the Emanuel African Methodist Episcopal Church in Charleston, South Carolina. Police contend the attack was racially motivated. Roof faces nine counts of murder in state court and dozens of federal charges, including hate crimes.

— May 23, 2014: A community college student, Elliot Rodger, 22, killed six people and wounded 13 others in shooting and stabbing attacks in the area near the University of California, Santa Barbara, campus. Authorities said he apparently shot himself to death after a shootout with deputies.

— Sept. 16, 2013: Aaron Alexis, a mentally disturbed civilian contractor, shot 12 people to death at the Washington Navy Yard before he was killed in a police shootout.

— July 26, 2013: Pedro Vargas, 42, went on a shooting rampage at his Hialeah, Florida, apartment building, killing six people before being shot to death by police.

— Dec 14, 2012: In Newtown, Connecticut, an armed 20-year-old man entered Sandy Hook Elementary School and used a semi-automatic rifle to slay 26 people, including 20 first graders and six adult school staff members, before killing himself.

— Sept. 27, 2012: In Minnesota's deadliest workplace killing spree, Andrew Engeldinger, who had just been fired, pulled a gun and fatally shot six people, including the company's founder. He also wounded two others at Accent Signage Systems in Minneapolis before killing himself.

— August 5, 2012: In Oak Creek, Wisconsin, a gunman killed six worshippers at a Sikh Temple before taking his own life.

— July 20, 2012: James Holmes, 27, killed 12 people and wounded 70 in Aurora, Colorado, movie theater.

— April 2, 2012: Seven people were killed and three were wounded when a 43-year-old former student opened fire at Oikos University, in Oakland, California. One Goh was charged with seven counts of murder and three counts of attempted murder but psychiatric evaluations concluded he suffers from long-term paranoid schizophrenia and is unfit to stand trial.