On Thursday evening, the Massachusetts State Police took to social media to share the extent of the gas emergency spreading across the Merrimack Valley.

But in so doing, they also shared the bookmarks bar at the top of the browser window — with some surprising entries.

The bookmarks raised more than a few eyebrows on Twitter, since they included the virtual meeting-places of several activist groups. Some activists felt it offered proof the police conduct unwarranted surveillance, particularly of organizations on the political left.

At 6:26 p.m., the state police's official Twitter account shared an image of a computer monitor showing the locations of 39 fires and explosions.

A screenshot of a now-deleted tweet from Mass. State Police, depicting confirmed fires and explosions in the Lawrence/Andover/North Andover area.

But whoever posted the image forgot to use a "crop" tool. So the image included the browser's bookmarked links, including several sites run by left-wing activist groups.

A closer-up look at a map tweeted out by Mass. State Police, inadvertently revealing bookmarks on the browser.

Among them were the Facebook groups for Mass. Action Against Police Brutality (MAAPB), which organizes protests and reposts stories of Americans killed by police; the Coalition to Organize and Mobilize Boston Against Trump (COMBAT); and other activist organizations. The "Resistance Calendar," which shares upcoming anti-Trump protests in Boston and nationwide, was also bookmarked.

State police deleted that first tweet, and another image they shared an hour later was cropped. But some shared screenshots of the original, suggesting the saved sites were evidence of unreasonable police attention focused on political speech.

In a statement, state police did not deny that they bookmarked these pages for monitoring, saying they have a responsibility to prepare for "all large, public gatherings."

The statement continued: "We, obviously, need to know if large numbers of people, for whatever reason, are going to be on public roadways or public spaces, so that we may ensure the safety and rights of those who have gathered as well as of the members of the public around them."

But some aren't satisfied with that argument.

"I wasn't surprised — but I was appalled," said Kade Crockford, director of the Technology for Liberty program at the Massachusetts branch of the ACLU. "American law enforcement has, for a very long time, targeted dissidents. A lot of people like to believe those tactics ended. But that's not true — and actually, after 9/11, they've seen a substantial resurgence."

Crockford observed that the second map tweet from the state police's account mentioned it was taken at the Commonwealth Fusion Center, an information-gathering nerve center in Maynard.

That center opened in 2005 under Gov. Mitt Romney, with the stated aim of improving the state’s "ability to fight crime and terrorism by analyzing data from a variety of sources."

Crockford said these institutions of "intelligence-led policing" have shown little success in preventing terrorist violence. "But what they have done, unfortunately, is marshal their substantial resources ... to keep track of the activities of perfectly law-abiding organizations that are expressing their First Amendment rights to organize and protest."

A 2015 ACLU report found that the state's other fusion center, the Boston Regional Intelligence Center, or BRIC, prepared intelligence reports on antiwar activists and elected officials.

Crockford pointed to a 2012 Senate subcommittee report that found that fusion centers hadn't contributed to federal counterterrorism efforts, and that they generated intelligence "of uneven quality — oftentimes shoddy, rarely timely, sometimes endangering citizens' civil liberties... and more often than not unrelated to terrorism."

Leaders from the affected groups did not respond immediately to requests for comment.

But it's worth noting that COMBAT and MAAPB are both small organizations, with fewer than 10,000 "likes" between them. Neither page lists any forthcoming events, and COMBAT has not published anything on its Facebook page since last November.

The state police statement pushed back on any claim of bias, saying, "We do not collect information about — nor, frankly, do we care about — any group’s beliefs or opinions." It called this kind of monitoring "a common – and common-sense – function of any police department."