A southern Illinois farmer's wife pleaded guilty Tuesday to plotting federal bankruptcy fraud and agreed to cooperate with authorities in a case connected to the unsolved slayings of a potential witness and his wife.

Margaret Diekemper, 64, pleaded guilty to a charge that she conspired with her husband to commit bankruptcy fraud. In return, prosecutors promised to drop 22 other felony counts during sentencing Feb. 9. The conspiracy count carries a possible five years in prison and up to $250,000 in fines.

As part of her plea deal, Diekemper agreed to cooperate with authorities, both by testifying about and disclosing to investigators "all criminal activity about which she knows." She also "will do all things deemed necessary" by federal prosecutors and investigators probing "activities in which the defendant is involved in or about which she knows," according to her plea agreement.

The plea agreement does not specifically say that Diekemper has agreed to testify against her husband.

Joseph Diekemper is scheduled to go on trial in January on charges that he defrauded the couple's creditors and others by lying about — and often hiding — millions of dollars in real estate and farm equipment.

Authorities also have been investigating the deaths of two people found shot to death last year on property where authorities say Joseph Diekemper stashed a tractor behind a false wall in an outbuilding.

The unsolved April 2007 killings of George and Linda Weedon came just a couple of days after George Weedon approached the FBI about the tractor and told an investigator he worried Joseph Diekemper would burn down his house if he ever found out, according to an FBI memo filed in the fraud case.

When the Weedons' bodies were found, their rental home was ablaze.

Margaret Diekemper's attorney did not immediately return a telephone message Tuesday from The Associated Press.

As part of the plea deal, Margaret Diekemper will not be prosecuted federally in southern Illinois for any crimes detailed by her cooperation.

An attorney for Joseph Diekemper, Gilbert Sison, suggested in a court filing last week that he and a federal prosecutor have been negotiating a potential plea deal, leaving "the distinct possibility" there'd be no need for a trial.

Diekemper has been jailed since July, when a federal judge revoked his bail after finding he had two rifles. His wife is free on bond.