In a letter sent to the minister on Friday, Casey advises MacKay that he is "particularly concerned" over the lack of indication that MacKay or his office "are taking any steps" to address the question of whether senior PMO staffers, Conservative senators and party operatives may have violated the Parliament of Canada Act.
"As you are aware, Section 4 of the Department of Justice Act places an explicit duty on you, as Minister of Justice and Attorney General to 'see that the administration of public affairs is in accordance with law.'"
To that end, he asks MacKay to provide "a detailed list" of what actions he has taken to fulfill his "statutory obligations."
According to MacKay's office, the minister has yet to receive the letter.
In a statement provided to CBC News, MacKay said it was "disingenuous to go to the press the day the letter was sent, knowing it would not have been delivered yet," and notes that as his party's justice critic, and a lawyer himself, Casey "surely knows that the Public Prosecution Service of Canada (PPSC) is an arms-length, independent agency."
Given that independence, he concludes, "Mr. Casey’s letter is better addressed to the Director of Public Prosecutions.”
Meanwhile, in a separate letter to RCMP Commissioner Bob Paulson, Casey says that he and many of his Parliamentary colleagues remain "deeply troubled" over the contents of those incendiary court files from last November, particularly the now notorious email exchanges amongstPMO staff, including then-chief Nigel Wright.
As such, he wants the RCMP to investigate whether a promise for payment was, in fact, made to Duffy by someone with the authority to transfer party funds.
"It is our belief that such an action may have violated Section 16 of the Parliament of Canada Act, or may constitute a conspiracy to violate the act, and could therefore potentially constitute an indictable offence," the letter concludes.
In an interview earlier this week, former House law clerk Rob Walsh suggested that the RCMP could have better luck bringing charges under the parliamentary law than the criminal code.
"The evidentiary burden I think is less (under the act) and, to that extent, it ought to be an easier task to prosecute," he told the Canadian Press.
Read the full text of both letters here:
Mobile users, view the letters here.