More lapses in security and record-keeping surfaced Thursday at the warehouse where Philadelphia’s voting machines are stored, prompting city officials to pledge — for the second time in less than a week — that they would beef up security amid an investigation into the theft of a laptop and USB drives from the facility.

A lack of surveillance footage from inside the warehouse has stymied investigators seeking to track down the thief. No cameras had been installed there despite an earlier request from employees to do so, according to sources familiar with the matter who were not authorized to discuss it publicly.

And while the city had vowed Wednesday to enhance security at the site, a reporter with WHYY’s Billy Penn entered the warehouse unhindered the next morning and spent several minutes walking among rows of voting machines before employees noticed and asked him to leave. He later posted a video to Twitter.

Meanwhile, the sources said, an ongoing inspection of those machines, launched after the theft to ensure that none had been compromised, has turned up more than 20 so far with serial numbers on their seals that do not match records kept by elections officials. They blamed the discrepancy on a logging error and do not believe it is evidence of tampering.

With those missteps mounting, city officials hastened to assure the public that they have every confidence that the integrity of the election had not been compromised by those developments — even as President Donald Trump’s campaign seized on them to sow doubt.

A spokesperson for Mayor Jim Kenney, responding to the video posted by the Billy Penn reporter, said Thursday that an around-the-clock police presence had now been stationed outside the warehouse and strict log-in procedures for those entering or exiting the building had been put in place. The mayor had pledged a day earlier to make all police resources available to find who stole the missing technology.

So far, police have discovered no evidence to suggest the thefts were related to the election, said sources briefed on the status of their probe. Aside from the missing laptop and USB drives, some smaller personal items were taken and stray objects appeared to have been moved around and left behind by the intruder, they said.

The employee whose laptop was stolen, an onsite technician for the company that supplies the voting machines, noted its theft on Monday and reported it to his superiors, the sources said. But it was not until two days later — once elections employees noticed the USB drives were also missing — that the matter was reported to police.

Nick Custodio — a deputy to Lisa Deeley, chair of the city commissioners, who oversee elections — declined to explain that apparent delay Thursday, citing the ongoing probe.

Still, a Trump campaign staffer tweeted a news story about the thefts and video of Thursday’s incursion into the warehouse by the reporter.

“Unbelievable!” the staffer, Mike Roman, wrote. “No security for voting machines How can we trust the results now?”

Roman — a Republican operative known for his role promoting a video of the New Black Panther Party standing outside a Philadelphia polling location during the 2008 election — falsely claimed on Twitter earlier in the week that Trump poll watchers had been turned away from city polling locations.

By Thursday afternoon, even some Democrats began to show signs of worry that the continued developments could needlessly hinder voter confidence.

Gov. Tom Wolf said state officials were monitoring the situation and noted during a news conference in Harrisburg that he was “obviously concerned,” while, in Philadelphia, Bob Brady, chairman of the Democratic City Committee, balked when he learned the warehouse remained at least partially unsecured Thursday.

“That’s ridiculous,” he said. “They have got to fix that. … I hope they’re up to the task. I’d hate to see something happen to ruin this election because of ineptness on our part.”

He added he did not believe that would happen.

Meanwhile, police pressed forward quietly in their efforts to identify who stole the missing laptop and USB drives.

Sources briefed on the status of the investigation said a gym next door to warehouse reported having asked a suspicious man to leave the business Sunday, hours before the laptop is believed to have been taken.

The gym shares an access point with the voting machine storage facility in the privately owned complex in which both are housed. There were no signs of forced entry into the building and police believe the intruder may have entered through windows in the gym that were left open on the day of the theft, those sources said.

The laptop and memory sticks remain missing, but elections officials remain confident that neither could be used to interfere with voting Nov. 3.

In a statement Wednesday, Custodio said the laptop had been disabled remotely as soon as the theft was discovered. A spokesperson for the manufacturer of the voting machines said the USB drives are encrypted to prevent tampering and specifically matched with individual voting machines.

In an abundance of caution, Custodio said Thursday, elections staff have wiped, reprogrammed and retested all machines whose seals were found with mismatched serial numbers when compared with the warehouse’s records to ensure that they will be secure come Election Day.

Chris Deluzio, an elections integrity expert and policy director of the University of Pittsburgh’s Institute for Cyber Law, Policy and Security, said that with those precautions in place he doubted the machines could be interfered with on Nov. 3. All Pennsylvania voting machines have paper ballot backups to the electronic tabulation.

“Whatever new threat factor is introduced because someone got their hands on the thumb drives or the laptop, I think the existence of individual paper ballots is still a strong bulwark against technical errors or hacks that might affect the machines,” Deluzio said.

His bigger fear is how the theft will be publicly construed by partisans, political campaigns or foreign actors seeking to build mistrust in the system.

“There’s going to be lots of bad information out there,” Deluzio said. There’s going to be lots of stuff … to make [people] feel like their votes don’t count, when in fact nothing could be further from the truth."

Staff writer Mike Newall contributed to this article.