More than 48 hours after the worst mass shooting in modern U.S. history, police still don't have a motive for the horrific crime.

But a more complete profile of the killer is beginning to emerge.

Stephen Paddock, the Las Vegas shooter who killed 59 people at a country music festival Sunday night, worked over a 10-year period as a letter carrier for the U.S. Postal Service, an IRS agent and a defense auditor.

A spokeswoman for the federal Office of Personnel Management told the Associated Press Tuesday that Paddock's employment included two years as a mail carrier from 1976 to 1978.

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That was followed by a six-year stint with the Internal Revenue Service until 1984. And then he worked 18 months as an internal auditor for U.S. Department of Defense.

The latest revelation suggests the U.S. government should have an extensive file on Paddock, who not only worked directly for the government for nearly a decade but then worked another year-and-a-half for federal weapons contractor Lockheed Martin.

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With his institutional knowledge of how the federal bureaucracy works, Paddock was anything but the typical mass shooter. He would have been able to cover his tracks in the planning stages of his attack.

The Islamic State, or ISIS, has doubled down on its claim of responsibility for the attack, saying Paddock had converted to Islam in recent months and become a "soldier of the caliphate."

But given the rapidly degrading status of ISIS, some analysts believe it could be entering a new phase where it is willing to risk credibility in its propaganda messages in exchange for a short-term boost in its prestige among Islamic terrorists worldwide.

In other news, leaked photos of the scene inside Paddock's hotel room at the Mandalay Bay Resort appeared to show a note on a small table near the shooter's dead body. As of this report, no details have been released about the contents of the note.

Video everywhere

Meanwhile, Clark County Sheriff Joseph Lombardo says his office has partnered with the FBI on the investigation but still has not come up with a motive for the shooting.

Lombardo said at a Tuesday press conference that Paddock had set up cameras both inside and outside his hotel room, with at least one placed on a service cart in the hallway.

"I anticipate he was looking for anybody to take him into custody," he said. "The FBI took all digital and electronic evidence into custody and is evaluating."

Lombardo said he did not know if Paddock transferred any of the video he captured to any third parties in the U.S. or overseas before taking his own life.

"We've completed our investigation at the properties, three separate locations in Mesquite and Reno, at the hotel and the suspect's vehicle," he said.

An additional five handguns, two shotguns, electronics and "a plethora of ammunition" were found Tuesday on top of the approximately 30 guns uncovered Monday.

Ammonium nitrate fertilizer, used for bomb making, was also found in Paddock's vehicle.

The sheriff confirmed earlier reports that at least one of the rifles was modified with a "bump stock" device used to speed up the discharge of ammunition. Paddock had enough ammunition "to continue shooting a lot longer" than the nine minutes he fired on the concert goers but was engaged quickly by police and private hotel security.

The sheriff said his agency learned from studying other active-shooter operations, including the one at the Pulse Nightclub in Orlando, that it's better to go in quickly and engage the shooter than to wait for an army of police to arrive and seal off a perimeter.

The sheriff said the quick police action saved dozens of lives that potentially could have been snuffed out by a man with such firepower at his disposal. He had 17 guns and at least 1,000 rounds of ammo in the hotel room.

Girlfriend back in the spotlight

Also in the spotlight during the Tuesday press conference was the shooter's girlfriend, Marilou Danley. Her location is now confirmed to be in the Philippines, and Lombardo called her "a person of interest" who has not necessarily been cleared of charges as was widely reported Monday. She will be thoroughly questioned as soon as she returns to the U.S., which is expected later this week.

Ammonium nitrate, found in Paddock's car, is the same substance Timothy McVeigh used to blow up the federal building in Oklahoma City in the 1990s.

Danley will be asked about any knowledge she may have of this substance as well as other weapons used in the attack, and any plans her boyfriend may have shared with her.

In the weeks before the shooting, Paddock wired up to $100,000 to the Philippines for unspecified reasons, possibly to Danley or her family.

Danley may also be asked about her trips to Japan, the Philippines and Dubai in the Middle East.

Paddock did not have a Facebook account, which makes him unusual, compared to other 21st century mass shooters and terrorists.

"I assure you this investigation has not ended with the demise of Mr. Paddock," Lombardo said.

When asked if the shooter's motive had been determined, the sheriff said: "No. We are making progress, but I don't have complete answers yet. I anticipate substantial information coming in over the next 48 hours."

Paddock continued shooting for approximately nine minutes.

"The world has changed," Lombardo said. "Who would have ever imagined something like this? I would have never imagined it."

He said some victims were shot "outside the venue," and others were shot in the venue but continued to run away and died "several blocks" from the venue.

All but three of the 59 victims have been identified, Lombardo said.

"This individual was premeditated, it was preplanned extensively, and I'm sure he evaluated every one of his actions," Lombardo said. "I pray that a citizen who sees something says something. A citizen sees things and thinks it's trivial, 'Oh, I don't want to bother the police.' We ask you to bother the police, because housekeeping and other individuals could have seen something," but none of them reported anything unusual about what they saw in the room.

It's important, he said, because, "I don't know that there won't be future prosecutions.

"Did this person get radicalized, unbeknownst to us? And we want to identify that source.”