It was just one of the many mysteries surrounding the Las Vegas concert shooting: How did the gunman, perched up on the 32nd floor of the Mandalay Bay resort, fire off as many as 90 rounds onto thousands of concert-goers in just 10 seconds, killing 58 people and injuring hundreds?

Reporters Sadie Gurman and Mike Balsamo found the answer. Through sourcework, they learned that Stephen Paddock was able to carry out his assault in moments because he had used two “bump stocks,” devices that allow a semi-automatic rifle to repeatedly fire like a machine gun.

The hub for Las Vegas coverage has so far received more views than any other breaking news hub on APNews.

The scoop was part of an impressive week of coverage by staff in the Las Vegas bureau and across the AP that also included photographer John Locher’s dramatic images of police screaming for people to take cover as the gunman sprayed the crowd with bullets.

For their work in bringing critical details and images of the worst mass shooting in modern U.S. history, Gurman, Balsamo and Locher win this week’s Beat of the Week prize.

A little after 10 p.m. on Oct. 1, Locher learned of a potential shooting near the Mandalay Bay. He had already worked a full shift, but sensed that the shooting could be bad. He headed to the scene, getting close enough to hear police screaming for people to take cover. For the next 11 hours, he stayed where he was amid the chaos, making images that were among the few that showed the police response to the shooting.

The Vegas bureau mobilized as did staffers from California and as far away as London. Their collective efforts paid off with exclusives, from UGC footage from a concert-goer to interviews with survivors in the hospitals to images of the covered bodies of the slain being loaded onto the coroner’s vans.

Balsamo, who works in Los Angeles but quickly deployed to Nevada, and Vegas reporter Ken Ritter scored several scoops, including that Paddock’s girlfriend had arrived in LA and was being questioned by the FBI, and that he had wanted to set off a car bomb

In Washington, Gurman, who covers the Justice Department, got a tip about the bump stocks from a source. It was quickly confirmed by Balsamo from a separate source. The devices, which are legal to buy and replace the gun's stock, use the gun's own recoiling action to "bump" the trigger and fire again more rapidly than any human could.

Their scoop on Oct. 2 beat the New York Times by more than 24 hours. Within minutes, AP's Richard Lardner tracked down Sen. Dianne Feinstein on Capitol Hill and pressed her on the issue, because Feinstein had introduced legislation years earlier to outlaw the devices. The Times matched the detail at 12:07 p.m. on Oct. 4.

Gurman additionally was first to report that the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives would not re-evaluate the lawfulness of the devices, kicking the politically sensitive subject back to Congress to amend existing gun laws or pass a new one.

The impressive work was all pulled together into a dynamic breaking news hub on APNews. A team led by West Desk editor Katie Oyan organized the coverage on the site. It included many videos and photos from the scene. The hub has so far received more views than any other breaking news hub on APNews.

For their work to help the world better understand the shooting, Gurman, Balsamo and Locher win this week’s $500 Beat of the Week prize.