As information trickles out of from Las Vegas about the attack Sunday night, the new deadliest mass shooting in U.S. history, here’s what we know about the gun — or guns — believed to be used in the attack.

What kind of gun was used?

Police searched the gunman’s hotel room, from where he fired the shots, and found “a cache of weapons” including at least 10 rifles, Las Vegas Metropolitan police sheriff Joseph Lombardo told reporters. Several recordings taken as shots rang out capture the sounds of rapid gunfire, similar to that of an automatic weapon. Automatic weapons are designed to continuously fire ammunition with just one pull of the trigger.

CNN reported that officials suspect the gunman may have altered one of the rifles to have a trigger like an automatic weapon, which would allow rapid fire of gunshots.

Distance between the hotel room and music festival in the Las Vegas shooting.

Police have not said specifically what type of weapon was used, such as a military-grade rifle or a machine gun, or whether this was indeed a semiautomatic weapon modified to fire automatically. It is also not clear yet if just one or multiple of the guns found in the room were actually used in the attack. The weapon or weapons used needed to have sufficient range to reach from the suspect’s hotel room to the target of the Route 91 Harvest, a country music festival, which was located diagonally across an intersection.

How many are available in the U.S.?

The ATF is required to maintain a central database of all registered firearms, called the National Firearms Registration Transfer Record System (NFRTR), per the National Firearm Act enacted in 1934.

More than 300 million total guns exist in the United States, according to a 2012 report from the Congressional Research Service.

If an automatic weapon like a machine gun was used, around a half million such weapons exist in the U.S. as of February 2016, according to the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

Is the gun legal?

Officials have not said if the gun or guns used are automatic or semiautomatic weapons, each of which is subject to different regulations in the U.S. Essentially, both types of guns are legal, despite claims gun rights advocates have made about their being banned.

A federal law banning certain semi-automatic guns and “large capacity” ammunition magazines was signed in 1994 under President Bill Clinton. But this Federal Assault Weapons Ban expired back in 2004 and has yet to be reinstated. The Hughes Amendment, passed in 1986, prohibited the manufacture of any new machine guns from then on. However, automatic guns owned before then are still legal today as long as they’re registered and approved by the ATF.

Individual states are allowed to regulate their gun laws even further. But Nevada, the site of Sunday’s attack, has some of the most lax laws. Gun owners — those both with handguns and bigger rifles and shotguns — do not need a license to buy and own their firearms, and don’t need to register their guns with the state, according to the National Rifle Association. The state does not have any restrictions on machine guns and assault weapons, or on background checks for gun owners.

Under federal law, anyone looking to purchase a gun must submit fingerprints and photographs to the ATF and submit to an FBI background check. However, Nevada’s attorney general said in December 2016 he would not enforce or implement the requirement for universal background checks. This essentially cancels out the federal effort to restrict automatic weapons, and allows for gun sales to take place freely between private citizens.

Such guns have often been used in mass shootings

Semiautomatic weapons were used at Orlando’s Pulse nightclub in 2016, the Sandy Hook Elementary School in 2012, the movie theater in Aurora, Colorado, in 2012, and Columbine High School in 1999.

“Assault weapons are designed to maximize lethality; they are intended to kill as many humans as possible as quickly as possible,” says the Coalition to Stop Gun Violence on its website. “It should come as no surprise that perpetrators of mass shootings often use these types of weapons.”

Guns in general are responsible for around 12,000 deaths in the U.S. each year, which breaks down to about 93 people per day, according to Everytown for Gun Safety. The Gun Violence Archive, which classifies a mass shooting as one in which “four or more people selected indiscriminately, not including the perpetrator, are killed,” says the Las Vegas shooting is the 35th one in the nation this year.

This post was updated on October 3.

Photos via Google Maps, Getty Images / Ethan Miller