By Fergal Parkinson BBC correspondent in Boston

In the early haze of Sunday morning on Boston Common, a man silently weeps as, one by one, a solemn procession steps up to a podium and reads out the name of a child, holding up their picture.

Most of the people here are those children, now grown, who say they suffered sexual abuse by members of the Roman Catholic clergy.

Cardinal Bernard Law is the target of many people who say they were abused

Today, they are calling for the resignation of Cardinal Bernard Law, a senior member of the Roman Catholic Church in America and the man they say knew about the abuse and did nothing to stop it.

From the accusations and evidence that have emerged so far, the Roman Catholic church in Boston has been hit by this scandal worse than any city in the US.

Horrific stories

The level of abuse that took place here sometimes defies belief.

One priest has been accused of child rape by 130 different victims, and that is just one story of many.

For the last few weeks, as the depths of the scandal have emerged, more and more voices have been calling for a full and open criminal investigation.

They want to know how much of the priests' wrongdoing the Church was aware of and for how long it hid the knowledge and, worse, failed to remove the offenders from contact with minors.

We are using every tool that is available to us to get the documentation and the information that we need

State Attorney General Tom Riley

Now in a huge triumph for the victims and an unprecedented legal move for the state of Massachusetts, a grand jury has been appointed to investigate possible criminal charges against Cardinal Law and other senior members of the Church for their failure to protect children from the priests they supervised.

The Massachusetts Attorney General Tom Riley, who called for the grand jury investigation, said that the Catholic Church had failed the most vulnerable members of its community.

"For the decades that this has happened no-one in a supervisory role has stood up and said this is wrong," he said.

"Now we are using every tool that is available to us to get the documentation and the information that we need."

Protesters carried pictures of child victims - often themselves

The decision to appoint a grand jury is unusual for two reasons.

Firstly, under American law, it is almost impossible to hold someone in a supervisory role responsible for the actions of another person.

But more surprising is the geography of the decision: Boston has an enormous Catholic population with a strong political voice which in the past has shown unswerving loyalty to the Church.

'Extraordinary move'

Kevin Cullen, an author and journalist for the Boston Globe who has been investigating the scandal for a year, said: "This is the most Catholic city in America.

"The attorney general himself is a devout Catholic and now he has launched a criminal investigation against the Cardinal - I can't stress how extraordinary that is."

They are beyond criminal

Anne Hagan-Webb on US Church leaders

Victims of paedophile priests have welcomed the criminal investigation.

For some, it has given them the confidence to come forward for the first time and speak about their own experience.

The feeling among demonstrators was that Cardinal Law should be treated like any other citizen, and face up to his responsibility.

Bill Gately, who says he was abused for three years from the age of 14 by his parish priest, said: "If there are laws that he has broken then he should be prosecuted. There is no doubt about it."

Little optimism

Anne Hagan-Webb, who was a victim of child rape over a 10-year period, said: "They are beyond criminal."

"They knew and they set these people loose among children year after year."

Though no-one is optimistic that criminal charges against Cardinal Law and other Church leaders will ever stick, the investigation means that the Church is no longer able to withhold documents and evidence from the state: any attempt to do so would now lead to criminal conviction in itself.

And with the Church's files, letters and documents now open to investigation, this city is bracing itself for the next sordid chapter of this tragic scandal.