On Wednesday, Portland developer Stephen Mardigan pleaded guilty to illegal gambling, money laundering and filing a false tax return. As part of the plea agreement, Mardigan will turn over 18 properties he owns in the Portland area, including his mansion, pictured here, at 460 Baxter Boulevard.

A Portland man pleaded guilty Wednesday to running a multi-million dollar gambling ring for more than a decade and has agreed to turn over more than a dozen properties to the federal government.

Stephen Mardigan, 61, entered the plea at U.S. District Court more than a year after FBI agents seized hundreds of thousands of dollars in a series of raids that first brought the investigation to public light.

He faces charges of illegal gambling, money laundering and filing a false tax return.

Mardigan committed these crimes, court documents state, as the head of a high-stakes sports betting syndicate that had operated in Portland since at least 2003 and could spit out more than $2,000 in revenue in any single day. The FBI wiretapped two of his phones and caught him accepting illegal bets last spring, according to court records.

He could be sentenced to as many as 28 years in prison, and according to the U.S. Attorney’s Office, appears to be exposed to millions of dollars in fines. One of his lawyers, Bruce Merrill of Portland, declined to comment.

Mardigan pleaded guilty a week after the U.S. Supreme Court s truck down a federal law that bars gambling on sports, opening a path for states to eventually legalizing it.

As part of the plea agreement, Mardigan will also turn over 18 properties he owns in the Portland area, including the Baxter Boulevard mansion that he has long called home.

[FBI seizes nearly $849,000 in series of Portland raids allegedly tied to illegal gambling]

The residential and business properties in Portland, Cape Elizabeth, Westbrook and Gorham were among those named last April in court filings related to a controversial program that allows the federal government to take property it believes to be linked to a crime before charges have been filed. Some of the properties are worth more than $1 million and they likely amounted to one of the largest civil forfeiture case in Maine’s history.

But Mardigan turned over the properties as criminal, not civil, forfeiture, according Donald Clark, assistant U.S. Attorney for the District of Maine. A civil lawsuit against the properties — a mechanism that the federal government uses in civil forfeiture cases — remained sealed in federal court Wednesday.

Mardigan also agreed to forfeit more than $1.3 million and pay more than $1.3 million in restitution to the Internal Revenue Service. He has not yet been scheduled for sentencing.

For at least 14 years, Mardigan took bets on professional and college football, baseball, basketball, car racing and golf, according to court documents. Gamblers would allegedly call either his cell or home phone and place wagers between $30 and $10,000.

The FBI tapped his phones last spring and overheard 17 people placing bets, court records state. Agents later identified another 10 gamblers from betting sheets seized from Mardigan’s home.

Mardigan ran this business out of his house at 460 Baxter Boulevard and a used car dealership on Forest Avenue, court documents state. Over the years, it drew in millions of dollars

From 2009 to 2016, two unnamed gamblers paid Mardigan more than $4.6 million in losses, while he paid them more than $1.3 million in winnings, according to court filings.

Mardigan seems to have attempted to conceal these large movements of money as the business of Avenue Auto. To settle their debts, the two gamblers allegedly wrote checks for millions of dollars to the car dealership and were, in turn, paid winnings from its accounts, as well as in cash, according to court documents.

Credit: Jake Bleiberg

The 767 Forest Ave. business consists of two buildings. One has long appeared vacant and had some of its windows broken Wednesday, while a desk stacked high with papers was visible through the large windows of the second building.

Over six years, the dealership registered sales for 57 vehicles and brought in more than $11.3 million, according to court documents.

Court records state that Mardigan was helped in running the gambling operation by at least five unnamed people. The FBI seized money or property from four other Mainers in connection with alleged illegal gambling last spring, but there are no public criminal cases against them in federal court.

Assistant U.S. Attorney David Joyce declined to say whether or not there would be more charges related to the gambling ring.

Mardigan used his gambling profits to build on an existing real estate empire. Over the years, court records state, he laundered money through the purchase of 19 properties — including his nearly $1 million home and two waterfront homes in Cape Elizabeth now valued at more $1 million each.

[Portland homeless shelter among buildings FBI seeking to seize]

On the same day last spring that FBI agents were confiscating cash from Mardigan’s home, the federal government filed a civil lawsuit against 30 of his properties. The case remains sealed but its first four pages are publically available through the Cumberland County Registry of Deeds.

Mardigan is not turning over many of the properties in the civil suit to the feds. For instance, although they are named in the suit, his forfeiture agreement does not cover four Portland buildings that the city runs as a shelter for homeless families.

A city spokeswoman affirmed that the Chestnut Street complex was not included in the case and said that Mardigan has paid his taxes on the property in full.

Mardigan was released without bail following the Wednesday court proceedings. He has waived his right to appeal a prison sentence of less than 30 months.

Follow Jake Bleiberg at: @JZBleiberg.

Follow the Bangor Daily News on Facebook for the latest Maine news.