The FBI announced Friday that billboards would go up around Las Vegas asking anyone with credible information to phone 800-CALL-FBI.
Investigators have delved into gunman Stephen Paddock's personal life, political affiliation, economic situation and any potential radicalization but so far have no clear motive for what prompted Sunday's attack, authorities said.
More about the shooting rampage that killed 58 and injured nearly 500:
Paddock's arsenal also included tracer bullets that can improve firing accuracy in the dark, a law enforcement official told The Associated Press on Friday.
It wasn't clear whether Stephen Paddock fired any of the illuminated bullets during the high-rise massacre.
Paddock bought the .308-caliber and .223-caliber tracer ammunition from a private buyer he met at a Phoenix gun show last month, a law enforcement official not authorized to comment on the investigation said on condition of anonymity.
Tracer rounds illuminate their path so a gunman can home in on targets at night. But they can also give away the shooter's position.
Video images of the pandemonium when Paddock started strafing the country music festival showed a muzzle flash from his 32nd-floor room at the Mandalay Bay resort. But bullets were not visible in the night sky.
NRA PROPOSES REGULATIONS
The National Rifle Association is joining the Trump administration and top congressional Republicans in a surprise endorsement of a narrow gun restriction in the wake of the Vegas concert shooting.
The NRA said devices called "bump stocks" that allow semi-automatic rifles to perform more like fully automatic weapons should be "subject to additional regulations." The devices were found in Paddock's hotel room.
President Donald Trump said his administration is considering whether they should be banned. State lawmakers in Massachusetts and New York filed bills to ban the devices in those states
THE UNWITTING FIRST RESPONDERS
A group of firefighters driving back to their Vegas station after responding to a call for a minor car crash ended up being the first to respond to the shooting massacre.
Brian Emery recalled that gunfire rang out as hundreds of hysterical people swarmed the vehicle on the Las Vegas Strip.
It was pure coincidence that the Clark County Fire Department crew members on Engine 11 were the first on-duty emergency personnel to arrive at Sunday's shooting.
The surge of people forced Emery to stop driving, but he eventually inched the engine out and got it to a parking lot where the crew could start treating patients. The work continued until after sunrise.
58 WOODEN CROSSES
White crosses have been placed on the Las Vegas Strip for each victim of the concert shooting.
Retired carpenter Greg Zanis drove nearly 2,000 miles from the Chicago area to put up the 58 crosses Thursday afternoon.
The 66-year-old is known for installing the markers at the sites of other mass killings, including the Columbine and Sandy Hook school shootings and Orlando nightclub massacre.
He plans to keep the tribute up for 40 days before giving the crosses to the families of the victims.
Associated Press writer Michael Balsamo contributed to this report from Las Vegas.
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