SAN FRANCISCO » At the height of the financial crisis, bargain hunters would gather each week on county courthouse steps to bid on foreclosed properties throughout Northern and Central California. The inventory lists were long, especially in hard-hit areas such as Sacramento and Stockton. But the auctions were generally short affairs — often because real estate speculators were illegally fixing the bidding process.

In the past three years, federal prosecutors have charged 54 people and two companies in three states for bid-rigging during courthouse auctions of foreclosed properties. Most cases originated in California, the state with the highest foreclosure rate during the financial crisis. Nearly identical rings were also broken up in Raleigh, N.C., and Mobile, Ala.

Working in concert, the would-be buyers would appoint just one person to bid on each property on the auction block, thus securing the "winning" bid. Minutes after the official proceeding was over, they would then conduct an auction among themselves, often on the same courthouse steps.

That’s when a property’s true price would emerge. The conspirators would then divvy up the difference paid at the official auction and the private one.

Federal prosecutors say such schemes have operated for decades, once earning a few thousand dollars per property. But the explosion of foreclosures amid the country’s financial meltdown a few years ago upped illicit gains to millions of dollars. The scammers took money that otherwise would have gone to banks selling the foreclosed properties or beleaguered homeowners who should have been compensated.

The bidding investigations are being driven by a special task force established at the U.S. Department of Justice in the wake of the financial crisis to combat mortgage fraud. The probes aim to "stop those who engage in illegal conduct that thwarts the competitive process, and take advantage of American consumers when they are most vulnerable," said Assistant Attorney General Bill Baer, head of DOJ’s antitrust division in Washington, D.C.

Prosecutors say the circle of conspirators gradually widened at each courthouse: First-time buyers would be brought into the conspiracy as an increasing number of speculators attended the auctions. Those not in on the schemes were often pressured not to return by verbal harassment and, in some cases, physical jostling.

In the last two years, more than 30 people have pleaded guilty to participating in a series of courthouse bid-rigging conspiracies in Northern California counties. Another 11 have been busted in Central California. Similar prosecutions have been carried out in Alabama, where eight people have pleaded guilty in Mobile in the last two years. Five others have pleaded guilty in North Carolina since 2010 to operating a bidding conspiracy around Raleigh.

For many now going to prison, this is their first brush with the law.

Father and son Robert and Jason Brannon were each sentenced to 20 months in prison this month in Mobile, Ala., after pleading guilty to participating in 17 rigged bids. The two opened a real estate investment company in 2003, after Robert Brannon sold a portion of the family farm. When they began attending auctions to acquire rental properties, they discovered that some speculators were rigging the bids and joined in the conspiracy, according to court documents.

In addition to the jail time, the Brannons were ordered to pay restitution of almost $22,000 each, their cut from the rigged auctions.

In April, real estate investor Mohammed Rezaian pleaded guilty to participating in similar scams in Northern California. He has agreed to cooperate in the prosecution of other perpetrators and pay a fine of $213,000. He also faces a little less than two years in prison when sentenced sometime next year. Neither he nor his lawyers returned phone calls.

Federal officials say they expect to charge a few more people in the coming months but that cases are expected to soon drop off now that the heated foreclosure market of late 2008 and 2009 has cooled.

Madeline Schnapp, an economist with PropertyRadar, a company that tracks foreclosures, said sales at auctions have fallen from a height of about 30,000 a month to about 5,000 a month in California as government programs and new laws have made it more difficult for banks to begin foreclosure proceedings.

"There’s not much of a supply now," she said.

Paul Pfingst, a lawyer who represents another investor charged in participating in a Central California ring, says illegal temptation got the better of many speculators who couldn’t resist victimizing seemingly unsympathetic banks. His client, Andrew Katakis, is accused of participating along with four others in a $2.5 million conspiracy to rig bids in the Stockton area, which has led the nation in foreclosures.

"The amount of money and properties that were changing hands was staggering," said Pfingst, who maintains his client’s innocence. "It caused many people to cross from legality to illegality."