Cosby is facing felony charges of sexual assault.
They stem from accusations made by former Temple University basketball coach Andrea Constand in 2004. A probable cause affidavit filed by investigators alleges that Cosby "sought to incapacitate" Constand by giving her a mix of pills and wine that sent her slipping in and out of consciousness and left her unable to consent to sexual activity.
In a statement Monday, Cosby's attorneys claimed that the charges against their client were "illegally, improperly and unethically brought by District Attorney Kevin Steele and his office."
According to the statement, the charges "violate an express agreement made by the Montgomery County District Attorney in 2005, in which the Commonwealth agreed that Mr. Cosby would never be prosecuted with respect to the allegations of sexual assault made by complainant Andrea Constand.
"This agreement, made for the express purpose of inducing Mr. Cosby to testify fully in Ms. Constand's civil litigation against him, led Mr. Cosby to give deposition testimony in 2005 and 2006 without invocation of his Constitutional rights against self-incrimination. Now, to fulfill campaign promises, the newly-elected District Attorney has repudiated the agreement and has based these criminal charges on the very testimony Mr. Cosby gave in reliance on the Commonwealth's non-prosecution agreement," the attorneys said.
They further argued that the charges should be dismissed because of the delay in bringing them.
And they ask, in the case that the charges are not dismissed, that Steele and his office are disqualified from further involvement.
Constand is one of at least 50 women who have come forward to publicly accuse Cosby of assaulting them over four decades. He has said his accusers are lying, and denied any wrongdoing.
Pennsylvania law has a 12-year statute of limitations for sexual assault cases. In 2005, prosecutors declined to charge Cosby in the Constand case, citing a lack of evidence. But late last year, the new district attorney -- Steele -- was elected, and he swiftly reopened the case.
Cosby is scheduled to appear for a preliminary hearing on January 14. If eventually convicted, he could face a maximum of 10 years in jail.