WEST PALM BEACH, Fla. - Nearly a year before the national furor over foreclosures began, Lisa Epstein, a nurse, ran into three other amateur sleuths who separately were investigating shoddy practices at mortgage companies.

While meeting for the first time in November at an old one-story law office in this city, the four strangers compared notes and began to piece together the scope of the problem: All over the United States, big financial firms might have been using fraudulent paperwork to evict struggling borrowers from their homes.

Now tight-knit, the group is largely responsible for setting off the growing firestorm over foreclosures.

Epstein, a Fairfax County native who became an activist after she lost her job and became unable to pay her mortgage, launched a grass-roots movement against the country's largest banks, which are facing the prospects of billions of dollars in soured loans and legal expenses.

Joining her were Michael Redman, whose foreclosure blog drew the White House into the controversy, and Thomas and Ariane Ice, who run a boutique law firm that was the first to depose "robo-signer" Jeffrey Stephan of Ally Financial's GMAC mortgage unit in December.

In addition to trying to educate the public about the issue, the group had also been quietly passing along stacks of problematic documents to state and federal regulators, lawmakers, judges and law enforcement officials.

They pointed out that document processors such as Stephan had admitted in sworn depositions that they had signed off on up to 10,000 foreclosure documents a month, even though they had not reviewed them as legally required. They also shed light on foreclosure cases in which the paperwork appeared to have been backdated, forged or improperly notarized.

Now, at least five major mortgage companies have frozen some foreclosures. Attorneys general from each state have joined forces to investigate, and a federal task force is considering criminal charges in the matter. Some bank stocks have fallen on concerns that the issue of flawed paperwork could be a coverup for something even more serious. And economists worry that the fragile housing market, where one in four houses on sale is in foreclosure, could take a devastating hit.

Although the uproar over foreclosures might seem sudden, for the activists, it was a long time coming.

Epstein, 45, a George Mason University graduate who moved from the Washington area to Florida for the sunshine 13 years ago, first began to suspect something was wrong in February 2009 after she was served foreclosure papers without any acknowledgment that she had applied for a loan modification.

Redman, 35, said he knew there was a problem as early as January 2008, when he was trying to help his fiancee fight foreclosure and noticed that one of the key documents that proved ownership of the loan had suspicious signatures.

The Ices' eureka moment came late one night in early 2009 when Ariane was looking at the 700 cases in their database and noticed that a lot of the problematic paperwork had been signed by the same people.