US prosecutors, hearing her story, dropped the charges. An asylum officer interviewed her and determined she had a credible fear of persecution if she were deported to Haiti. But immigration officials kept her in jail, holding her in Boston and releasing her only last month after the Globe requested an interview.

“I was crying, crying, crying,” Alce said after a brown minivan dropped her off at South Station one day last month, still dressed in a gray prison sweatsuit and white sneakers. “They were just holding me here for no reason.”

Despite the high-profile release of hundreds of immigrants this week, immigration lawyers and advocacy groups say that thousands of immigrants like Alce — who have no criminal record and pose no threat to their communities — remain jailed by the nation’s sprawling immigration system, sometimes for prolonged periods.

The detainees are held for many reasons, but often they are merely awaiting a hearing before an immigration judge or waging an appeal, and lawyers say immigration officials instead should release them to their families.

Critics say detention is necessary to ensure that illegal immigrants are deported, but advocates argue that many of the roughly 30,000 detainees could be monitored in cheaper and more humane ways.

“We think that most people that are in detention right now can be let out,” said Laura Rotolo, staff attorney with the American Civil Liberties Union of Massachusetts. “Until now we have not gotten the sense that the administration was willing to do that.”

Immigrant advocates have pushed for years for the release of such detainees, without much success. Even a directive in 2011 asking Immigration and Customs Enforcement officers to focus resources on criminals and others considered priority cases did not result in major releases, advocates said.

But advocates recently began stepping up pressure on the Obama administration, seeing a prime political opportunity as the president and Congress attempt to hammer out legislation that could clear the way to legal status for some 11 million illegal immigrants nationwide.

The effort worries critics like Bristol County Sheriff Thomas Hodgson, whose agency detains immigrants for ICE. He said immigration officials should enforce the law unless it changes.

“We can’t keep marginalizing what the enforcement of our law is,” he said. “If everybody starts interpreting what their impression of the law ought to be, then we’re going to have problems with our democracy.”

This week, federal immigration officials, citing anticipated budget cuts forced by sequestration, released several hundred immigrants from jails across the United States. It ignited a political firestorm, cheering advocates but angering members of Congress and others who said the mass release could derail their efforts to craft immigration reform legislation.

Officials would not say if any immigrants were released in Massachusetts, but Suffolk and Bristol county jails said they were unaware of any sudden declines in the number of immigrant detainees.

Gillian Christensen, ICE spokeswoman, said immigration officials will keep trying to deport the released immigrants and has placed them on less costly forms of supervision to make sure the agency stays within budget. “All of these individuals remain in removal proceedings,” she said. “Priority for detention remains on serious criminal offenders and other individuals who pose a significant threat to public safety.”

Immigration advocacy groups, while heartened by the release, say they’ll continue to press for more.

Among those still detained this week was Ronei Ferreira-De Souza, a 36-year-old landscaper from Brazil who has been fighting to overturn a deportation order for five months from Plymouth County jail.

His lawyer, George Maroun, said Ferreira-De Souza is a church-going married man and the father of two US citizens with a stack of reference letters from friends who praise his work ethic and faith. And, his lawyer said, he has no criminal record, though he was once arrested for driving without a license.