Calling for a lighter sentence than federal prosecutors' recommendation of four years in prison, former state Sen. Dianne Wilkerson's attorneys have argued in court papers that the Roxbury Democrat has been "selfless," pointing to a letter in support of Wilkerson from a family member of Milena DelValle, the woman killed in the Big Dig tunnel collapse.

But prosecutors hit back in a Wednesday court filing, less than a day before a judge is due to sentence her. They argued she undercuts her own claims by having attempted to get a fee for referring the victim's family to an attorney.

Wilkerson's sentencing is scheduled for Thursday at 2:30 p.m. at the Moakley Courthouse. Wilkerson pleaded guilty in June to attempting to accept $23,500 in bribes in exchange for legislative action.

"What Ms. Wilkerson’s submission fails to disclose is the fact that two weeks after Ms. DelValle was killed in an accident, Wilkerson sought to obtain a referral fee for herself for referring the DelValle family to a Boston law firm," prosecutors wrote.

Fifteen days after DelValle was killed in the tunnel, Wilkerson asked the state Senate's counsel to inquire the state Ethics Commission whether she could accept a referral fee for "finding her constituent a lawyer," prosecutors charge. "The Ethics Commission advised that it might be a violation of State ethics law and 'was a very bad idea.'"

She did not press for the fee, prosecutors note, adding that "at the same time that Wilkerson was seeking advice about the referral fee, her common-law daughter-in-law (the mother of one of Wilkerson’s grandchilden [sic]), sought and received employment at the law firm to which Wilkerson referred the DelValle family."

The prosecutors, Assistant U.S. Attorneys John McNeil and James Dowden, wrote that if Wilkerson's efforts were "selfless" as she claims, "there would never have been a need for her to inquire about the ethics of receiving a lucrative referral fee."

In his letter of support, Duane Nelson, the brother-in-law of Angel DelValle, whose wife was killed in the Big Dig incident, said that in the days after the incident Wilkerson coordinated communications between the family and officials at all levels of government, and secured passports for the family to travel to Costa Rica for the burial.

"Please do not allow the press or the public to decide the fate of one who is basically good," Nelson wrote in the Nov. 15 letter. "Justice would require that you show to Dianne the same kind of caring, kindness and compassion that she showed to us and many others."

She has received 103 letters of support so far.

Separately, a Boston police officer who was present at the Dec. 22 testimony of a local contractor who allegedly bribed Wilkerson says he believes the contractor was untruthful in a portion of his testimony. The police officer, in court documents filed Wednesday by Wilkerson's defense attorneys, said contractor Azid Mohammed's testimony on his driver's license and interactions with Boston Police did not jibe with the Registry of Motor Vehicles' records.

Mohammed was under an immunity agreement when he testified, and the judge weighing Wilkerson's fate, Douglas Woodlock, had said he would take his Dec. 22 testimony into account when sentencing her.