Back in January 2015, protesters sympathetic to the Black Lives Matter movement stepped onto Interstate 93 in Medford and Milton, spread out across the roadway, and ground morning rush hour to a halt.

Now, the last remaining person to face prosecution and jail time in connection with those protests is out of legal jeopardy.

On Thursday, Middlesex County District Attorney Marian Ryan announced that she was dropping the lone remaining charge—conspiracy—faced by Jessie Lowell, a computer science graduate student at Brandeis.

Over time, the heated debate sparked by the so-called Somerville 18, and their counterparts who were arrested in Milton, has faded away. And so, with the exception of Lowell, had the charges faced by the participants, who resolved their cases in ways that avoided jail time.

For the record, Lowell didn’t actually block traffic that day. Instead, she acted as what she calls a “street medic," waiting on a patch of grass just off the highway to provide first aid to anyone who needed it.

She also was watching law enforcement’s response to the protesters, whose cause she supported.

"Racism is a very important issue, and the way black people are treated in this country is a very important issue," she told WGBH News earlier this week. "And as a white person, I think I have a moral responsibility to do something about them."

Prosecutors charged Lowell with trespassing and disorderly conduct, saying she’d aided and abetted the protesters and refused orders to leave the area where she'd been standing. (Lowell denies this.)

A second street medic who'd been with Lowell at the scene eventually cut a deal, admitting there was sufficient evidence to convict him and receiving probation and community service.

But Lowell refused to do that—because, she insisted, she’d done did nothing wrong.

"I walked onto some un-posted grass in an open area, not fenced in, to provide first aid if necessary, and to exercise my right to observe police behavior," Lowell said. "I attempted to obey police orders the best I could.... So yeah: I didn’t think I’d committed any crime."

In March, a jury agreed, acquitting Lowell of trespassing and disorderly conduct. But she still faced a second trial on a conspiracy charge, with the possibility of up to 90 days in jail if convicted.

Mark Stern, who represented Lowell through the National Lawyers Guild Mass Defense Committee, said earlier this week that he was perplexed by the DA’s determination to convict.

"The prosecution of one medic for observing police, and being available to provide aid...has now involved, on two misdemeanor charges, what I’d image would be tens of thousands of dollars in public resources." Stern said. "It’s absolutely inconceivable to me why they did this, why they’re continuing to do it.  

But on Thursday—one day after WGBH News contacted the Middlesex DA’s office about Lowell–Ryan filed a motion to drop Lowell’s case.

"Although there was probable cause for the charges to issue in this case," the motion stated," after reviewing the testimony and evidence presented during trial on the first two counts of the complaint, the Commonwealth has determined that it is not in the interest of justice to pursue the conspiracy charge."

Afterward, I traded emails with Lowell, who thanked her attorneys and said: “I’m thrilled and relieved that it’s finally over! It has been a long fourteen and a half months.”

For his part, attorney Mark Stern sounded gratified by the outcome—but also frustrated.

“All this shows,” he said, “is that they’ve been persecuting her for a year and a half without any sound basis for doing so.”