Las Vegas police say they still do not have a clear motive as they investigate the worst mass shooting in modern U.S. history.

At a Friday afternoon briefing, Undersheriff Kevin McMahill said they also are not clear what the gunman planned for the explosives found in his car. They are aware ISIS is claiming the 64-year-old shooter who gunned down 58 people attending a country music festival and injured nearly 500 but see absolutely nothing that supports that claim. Authorities are “very confident” there was just one shooter in the suite on the 32nd floor of the Mandalay Bay Resort hotel but “continue to investigate whether anybody else may have known about this incident before he carried it out.”

All the rumors and speculation being pushed out on social media are “not helpful to our investigation,” McMahill said curtly.

“Just because you think you know something doesn’t mean you do. If you have factual information, it would be helpful to us,” he said to the larger public watching the briefing on TV.

To that point, authorities plan to put up billboards throughout the area giving people a phone number to call if they know something that might be relevant to the crime. “We have not stopped and we will nto stop until we have the truth,” McMahill promised.

He acknowledged the frustration of the investigation, noting that perpetrators of planned-out attacks typically make their intentions clear in a note, social media post or phone call. Or, it becomes evidence when investigators mine their computer.

“Today, in our investigation, we don’t have any of that uncovered,” McMahill said. “I wish we did, and we will continue the investigation with tenacity.”

The police department has “not done a good enough job” of publicly recognizing the bravery of the hotel security guard who was shot in the leg when he went to investigate a door alarm that had gone off in the shooter’s suite, and notified police of the location of the shooter. “I want to clear the record: He is an absolute hero,” McMahill said.