The FBI launched an information campaign Friday that will include billboards throughout Las Vegas, appealing for public tips about the weekend shooting rampage that left 59 people, including the suspected gunman, dead.

The billboards will feature the slogan "If you know something, say something" followed by an FBI contact number,  FBI special agent in charge Aaron Rouse told reporters Friday in Las Vegas.

A memorial of 58 white crosses was erected in Las Vegas for the victims of as mass shooting o the Las Vegas Strip just south of the Mandalay Bay hotel.

The campaign is a measure of how little the authorities have unearthed as to why the suspect, Stephen Paddock, 64, opened fire from a room on the 32nd floor of the Mandalay Bay Hotel last weekend during a country music festival. In addition to those who died, nearly 500 others were injured.

Rouse said the information campaign is seeking "true knowledge" into how the killings unfolded and why.

"We will not stop until we have the truth," Rouse said.

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Undersheriff Kevin McMahill told reporters there is much about the shootings that they still do not know or understand.

He said investigators have followed up on a thousand leads that have helped build a better profile of the "madness of this suspect," including  his personal life, political affiliation, economic situation and any potential radicalization. "We still do not have a clear motive or reason why," he said.

McMahill said authorities are confident there was not another shooter in the room that night, but could not rule out that someone else may have known about the plan before the gunman carried it out.

McMahill also said authorities are aware that the Islamic State has claimed responsibility for the attack, but so far there is no evidence that the extremist group played any role.

Earlier Friday, Scott Armstrong, a Reno, Nevada, car dealer, said Paddock confided in him about relationship troubles when the would-be gunman stopped in looking to buy a car about two months ago.

“Somehow or another we ended up talking about bad relationships, and he confided that he was depressed and his life was miserable,” Armstrong said. “It just struck me as really odd that somebody would say that.”

Paddock, unshaven and dressed casually but not disheveled, didn’t elaborate on his relationship troubles, and Armstrong didn’t pry. He didn’t smile, and he “wasn’t very pleasant to talk to,” he said, the Associated Press reported.

“I could tell he was really down or something,” Armstrong said. “I just told him, I said, ‘Hey I’ve been in some bad relationships myself. It’ll get better. Tomorrow will be a better day than today.’ “

Armstrong said he’s talked with FBI agents about his recollection.

Contributing: Associated Press