About 150 people from across Massachusetts marched outside The Boston Globe on Monday to protest a Spotlight series on the dismantling of the state’s mental health system and the sometimes tragic consequences.

Waving placards and chanting slogans, protesters said that the multipart series — titled “The Desperate and the Dead’’ — has contributed to the impression that mental illness is often linked to violence.

“Most mentally ill people are not violent people,’’ said Sarah Ahern, a 44-year-old woman from Greenfield who said she has suffered from posttraumatic stress disorder, anxiety, and depression.

Twelve people were arrested on trespassing charges, police said. Globe security said the protesters sat down, blocked the front entrance, and refused to leave.

The Globe has published two installments of the ongoing series since June.

Spotlight Team editor Scott Allen, who met with several protesters outside the Globe building, said the series demonstrates great empathy for those with mental illness while chronicling sweeping changes that have left many of the most vulnerable — and potentially violent — without adequate care and supervision.

“We documented 139 victims of homicide at the hands of people with mental illness in Massachusetts, which is not a small number,’’ Allen said of the Spotlight investigation, which looked at murders dating back to 2005.

“But regardless of the absolute number, many of them were preventable deaths,’’ Allen said. “The key point is that, with a better mental health care system, some of these lives could have been saved.’’

One of the major conclusions of the series is that Massachusetts failed to develop a broad, effective system to care for the mentally ill after closing state psychiatric hospitals, many of which were viewed as antiquated and inhumane.

The Spotlight Team found that, since 2005, more than 10 percent of Massachusetts homicides in which a suspect was identified were allegedly committed by people who had a history of mental illness or clear symptoms.

The protesters, many of whom said they have received psychiatric treatment, said the series overstated the connection between mental illness and violence.

“That’s all people walked away with,’’ said Justin Brown, one of the organizers of the protest. “It demonizes us in much the same way as when Donald Trump says there are murderers coming across the border.’’

Globe editor Brian McGrory, who also met with the demonstrators, said: “We heard their perspective quite clearly, and it was important for us that we did. The bottom line, though, is that we want what they want, which is vastly better care for those with mental illness. That’s what this series is about.’’

Two buses brought the protesters to the Globe, where they called out the names of hundreds of mentally ill victims, some of whom died while in restraints. The protesters placed flowers for the victims on the ground.

They chanted, “No more lies,’’ and carried signs that read “Fear mongering does not heal,’’ and “Stop scapegoating me!’’

Many protesters acknowledged that they had not read the entire series, and one marcher said she had joined the demonstration primarily as a way to criticize the state’s mental health system, which she described as understaffed and underfunded.

“There is no system,’’ said Joanne Grady of Duxbury. “It’s broken.’’

Brian MacQuarrie can be reached at brian.macquarrie@globe.com.