The AR-15: the most popular rifle in the US

Aurora, Sandy Hook, San Bernardino and now Orlando - in each of these places, an assailant wielding an AR-15 rifle has claimed the lives of school children, moviegoers, people celebrating Christmas or a night out.

Designed by ArmaLite for the US army and originally produced by Colt in the 1960s, the AR-15 is the most popular rifle in the United States, according to the National Rifle Association (NRA). The semi-automatic weapon is prized for being lightweight, its capability of holding high-capacity magazines and its relatively easy customization.

Newtown lawyer: 'the gold standard'

For a decade, it was effectively illegal to purchase a new AR-15 under statutes of the Federal Assault Weapons Ban (AWB). Following the 1989 death of five children and injuries to more than 30 people including a teacher in Stockton, California at the hands of a man wielding an AK-47 semi-automatic rifle, the US government sought to prevent the kind of mass shootings that the accuracy and speed of guns like the AR-15 and AK-47 can facilitate.

President Bill Clinton signed the AWB into law in 1994 as part of a larger crime bill. The ban on assault weapons was given an initial time frame of ten years, and in 2004 the US Congress failed to renew it.

Since retaining its full legal status, it has become the "gold standard for the mass murder of innocent civilians," according to a lawyer representing the families of victims who died at Sandy Hook Elementary School in Newtown, Connecticut, who are suing the gun's manufacturers for negligence.

In light of the tragedy at Sandy Hook, in which 20-year-old Adam Lanza fatally shot 20 children, six staff members and himself in December 2012, the AR-15 cannot be sold in Connecticut, New York, and Maryland, among other states.

While the National Rifle Association has argued that the AR-15 is useful as a hunting rifle, according to a host of both anti- and pro-gun websites, most hunters eschew it as unhelpful in the pursuit of game at a distance.

Terrorists urge followers to commit shootings

Terrorist groups including the "Islamic State" (IS) have called on their followers to take advantage of lenient US gun laws to launch attacks. According to media reports, shooter Omar Mateen vowed loyalty to IS before killing at least 50 people and wounding 53 others at the gay nightclub Pulse in Orlando, Florida, early Sunday morning before he was shot dead by police.

Despite being targeted by an FBI investigation in 2013 for terrorist ties, Mateen was later dismissed as not constituting "a substantive threat." He legally purchased his weapons, at least one of them an AR-15, a few days before the shooting.

According to USA Today, during its 2013 address to US Congress the National Shooting Sports Foundation estimated that between 5 and 8.2 million assault-style rifles are privately owned across the country. When online magazine Slate conducted a survey in 2012, it surmised that some 3.3 million of those were AR-15.