LAS VEGAS (KLAS) – Before they hijacked airplanes on 9/11, 20 years ago, Osama Bin Laden’s terrorists made multiple visits to Las Vegas. Two decades later, we still don’t know for sure why they were here.

Former Clark County Sheriff Jerry Keller says there had been almost no discussion of Las Vegas as a possible target for attack by the likes of al-Qaida prior to the events of 9/11, but in the hectic hours after the hijackings, Keller and the other agency heads who gathered at FBI headquarters started thinking the unthinkable.

“Who knew (if Vegas was a target)?” Keller remembered. “There were still planes flying when we were making this decision, they hadn’t all landed yet.”

Keller said at the time terrorism was thought to be a foreign state issue

Within days of the attacks, local anxieties increased as the FBI shared classified information with Keller, including details still not widely known.

“(The terrorists) were here,” said Keller. “There was another guy they tracked in Arizona who was planning to come across the dam. Nothing happened from that but that was the early information.”

Former Metro Sheriff Jerry Keller recounts the time 9/11 terrorists spent in Las Vegas.

Ringleader Mohammed Atta and at least four of the other 19 hijackers made six visits to Las Vegas between late May and mid-August of 2001.

Atta, who piloted the first plane into the world trade center, flew to Las Vegas on June 28, rented a car, then spent 90 minutes online at an internet cafe across from UNLV.

The following day, Atta checked in at the Econo Lodge on Las Vegas Boulevard, within shouting distance of the FBI office, put a do not disturb sign on his door, and stayed two nights in a room that faced the Stratosphere Tower. When Atta returned his rental car on July 1, it had 110 miles on it.

It raises the possibility that someone in Southern Nevada may have helped the terrorists.

“Without a doubt,” said Bill Young, who was in charge of special ops teams for Metro and would go on to become sheriff. “I’m guessing, whoever was here also came from somewhere else and they met up. We just never figured out who they were.”

Former Metro Sheriff Bill Young discusses the 9/11 investigation.

Young’s detectives and FBI agents poured thru mountains of hotel records, rental car receipts, and surveillance videos to document the terrorists’ movements.

Tipsters say at least one terrorist received lap dances at Olympic Gardens, a since-closed strip club. Other terrorists sipped coffee across from UNLV and partied and gambled at casinos. Many leads from the public could not be confirmed. The biggest questions remain unanswered:

“Were they in pre-op planning for something here in Las Vegas?” Young recalled. “Were they here to plan ops for somewhere else? Were they here to have a last hurrah before they go get their 72 virgins or whatever they get? I’m not sure, not sure anyone can say definitively.”

The hijackers weren’t the only visitors of note in the summer of 2001. On 9/11 itself, more than 100 members of the Saudi royal family and their friends the Bin Ladens were staying in Las Vegas, mostly at Caesars Palace and the Four Seasons. Osama Bin Laden’s sister was well known at the Bellagio.

The Saudis were grounded along with everyone else but after being interviewed by the FBI, were cleared to leave aboard three special charter flights.

“They were here. They’re always here,” said Young. “They’ve been here since. Some of them are gamblers, high rollers, good customers.”

In the 20 years since 9/11, police in Las Vegas and elsewhere have undergone vast changes in how to prepare for and respond to possible terrorist attacks. Metro has greatly enhanced its own intelligence capabilities.

What has also changed is the nature of the threat. Homegrown domestic terrorists are as much or more of a threat as the foreign variety, according to Sheriff Joe Lombardo.

“The paradigm has changed a lot over the years since 9/11,” said Lombardo. “The crux was foreign terrorism. And then now the proliferation of like-minded groups via the internet and other social media spaces coming together, and domestic terrorism has become readily prevalent.

In the above video, Metro Sheriff Joe Lombardo discusses the ever-changing threat of terrorism.