LAS VEGAS — A laptop found inside the Las Vegas gunman’s hotel suite after he carried out the deadliest mass shooting in modern U.S. history was missing a hard drive, a federal official told The Associated Press on Wednesday.

Investigators suspect gunman Stephen Paddock removed the hard drive from the laptop after opened fire from his high-rise suite at the Mandalay Bay hotel-casino into a crowd at a country music concert, killing 58 people and wounded hundreds of others, the official said.

The official wasn’t authorized to discuss the matter publicly and spoke to the AP on condition of anonymity.

The hard drive hasn’t been found, according to the official, and the absence of digital clues adds yet another puzzling aspect to the investigation as authorities try to figure out what might’ve led the 64-year-old high-stakes gambler to commit the mass killing. Investigators have examined his politics, finances, any possible radicalization and his social behavior — typical investigative avenues that have helped uncover the motive in past shootings — and there’s still no clear motive.

On Wednesday, authorities also estimated that the costs of police, fire and other emergency services related to the massacre were projected at about $4 million and climbing.

The disclosure came amid pledges by the federal government to provide $1 million, and from the state of Nevada to pay $600,000 to defray costs stemming from the Oct. 1 shooting.

Las Vegas police Officer Laura Meltzer provided what she called a preliminary figure of $3.5 million for department costs associated with the worst mass shooting in modern U.S. history.

“We still have a lot of resources devoted to the investigation,” Meltzer said. “We still have people working overtime and around the clock on it.”

The amount spent on overtime to date amounts to more than half a percent of the annual Las Vegas police budget.