CHICAGO >> The way the FBI tells it, William Rosario Lopez put on a surgical mask and walked into the Connecticut convenience store looking to the world like a typical pandemic-era shopper as he picked up plastic wrap, fruit snacks and a few other items. Then, when the only other customer left, he went to the counter, pulled out a small pistol, pointed it at the clerk and demanded that he open the cash register.

The scene, the FBI contends in a court document, was repeated by Lopez in four other gas station stores over eight days before his April 9 arrest. It underscores a troubling new reality for law enforcement: Masks that have made criminals stand apart long before bandanna-wearing robbers knocked over stagecoaches in the Old West and ski-masked bandits held up banks now allow them to blend in like concerned accountants, nurses and store clerks trying to avoid a deadly virus.

“Criminals, they’re smart and this is a perfect opportunity for them to conceal themselves and blend right in,” said Richard Bell, police chief in the tiny Pennsylvania community of Frackville. He said he knows of seven recent armed robberies in the region where every suspect wore a mask.

Across the United States, masks have become more and more prevalent, first as a voluntary precaution and then as a requirement imposed by governmental agencies and businesses. And people with masks — as well as latex gloves — have found their way into more and more crime reports.

Just how many criminals are taking advantage of the pandemic to commit crimes is impossible to estimate, but law enforcement officials have no doubt the numbers are climbing. Reports are starting to pop up across the United States and in other parts of the world of crimes pulled off in no small part because so many of us are now wearing masks.

In March, two men walked into Aqueduct Racetrack in New York wearing the same kind of surgical masks as many racing fans there and, at gunpoint, robbed three workers of a quarter-million dollars they were moving from gaming machines to a safe. Other robberies involving suspects wearing surgical masks have occurred in North Carolina, and Washington, D.C, and elsewhere in recent weeks.

The problem isn’t limited to robberies. In the troubled Cook County Jail in Chicago, the virus has led to at least nine deaths and sickened hundreds of inmates and correctional officers. Staffers must wear masks and inmates are issued a new one every day — a policy that helped one inmate escape on May 2.

Jahquez Scott, jailed on a gun charge and for violating his bond in a drug case, has tattoos of a small heart on one cheek and what looks like a blood-dripping scar on the other. But when he wore a mask, he posed as Quintin Henderson — who doesn’t have tattoos on his face and was scheduled to be released, authorities said.

Scott made it out, though he was captured a week later.

In addition to rare jailbreaks, the prevalence of masks in society has created other problems for law enforcement. Before life in a pandemic, masked marauders had to free their faces immediately after leaving a bank or store to avoid suspicion once in the general public. But it came with the risk of being photographed and identified through omnipresent surveillance cameras and cellphones.

These days, they can keep the masks on and blend in easily with or without being “captured” in images.

“The video is much less useful if we are unable to see a face,” said Carlos Marquez, a detective division commander in the Los Angeles County Sheriff’s Department, in an email.

It’s leaving law enforcement without a crucial crime-solving tool.

“Guys are like, ‘OK, I have to wear a mask, the police are not going to stop me on the way to a crime and back from a crime wearing a mask,’” said Brendan Deenihan, chief of detectives for Chicago Police Department. “Now if you are going to commit a crime you can leave your house with a mask on and drive for an hour.”

With everyone basically incognito, would-be witnesses might not notice someone acting differently, and that would make it harder to get a good description or identification of the suspect, said Eric Nuñez, chief of the Los Alamitos Police Department in Southern California and president of the California Police Chiefs Association.

It’s less likely now that other shoppers would “stare at them, just making mental notes of what they look like,” Nuñez said. “If they look like everybody else walking in, they may not do that at all.”

It’s a real problem for clerks and tellers, such as Tiffany Becker, who manages a Valero convenience store in Shenandoah, Pennsylvania, where a number of stores in the area have been robbed by mask-wearing gunmen recently.

“Before I would have called the police because having a mask wasn’t normal. Now it’s normal,” Becker said. “It’s scary because you can’t tell who is safe and who’s not.”

Even when investigators identify suspects, the protective gear makes putting cases together all that much more difficult. The same latex gloves more people are wearing to protect themselves from picking up the virus will mean fewer fingerprints at crime scenes.

“In the past if you did a search warrant and you found surgical masks, that would be highly indicative of something (suspicious),” said FBI Special Agent Lisa MacNamara, who investigated the string of robberies in Connecticut that led to the arrest of Rosario Lopez. “Now everybody has masks or latex gloves.”

But the reverse can also be true.

MacNamara and her team’s investigation was made easier when his alleged accomplice went into the stores “acting as a lookout or ‘casing’ robbery locations.”

The accomplice hadn’t worn a mask.