OTTAWA -- The Public Prosecution Service of Canada is involved in allegations of improper government influence in two major cases: the prosecutions of Vice-Admiral Mark Norman over allegations he leaked secrets to a shipyard and of SNC-Lavalin on charges of bribery and corruption in Libya.

Here are five things to know about the prosecution service and its independence:

What is the Public Prosecution Service?

The service is "a national, independent and accountable prosecuting authority" whose mandate is to prosecute federal offences as well as provide legal advice and assistance to law enforcement.

The office may prosecute in cases covered by 250 federal statutes, although it only regularly uses about 40 of those. Its cases include money-laundering, organized crime, terrorism, and regulatory offences. Many of its cases involve drug charges under the Controlled Drugs and Substances Act. It also handles Criminal Code charges in the three territories, cases that are prosecuted by provincial Crown attorneys in the provinces.

As of last spring, the service had over 1,000 employees. It is headquartered in Ottawa with regional offices across Canada.

Formerly the Federal Prosecution Service, the 2006 Director of Public Prosecutions Act made the service formally independent of the Justice Department -- it answers to the same minister but isn't part of the same bureaucracy.

What was the point of that?

The prosecution service was created on Dec. 12, 2006 following a Conservative campaign promise that it would be free of political interference. This was after the sponsorship scandal, and the Tories had been elected partly on a promise that they'd clean up political corruption.

"There's going to be a new code on Parliament Hill," prime minister Stephen Harper said at the time. "Bend the rules, you will be punished; break the law, you will be charged; abuse the public trust, you will go to prison."

Who's in charge of it?

Kathleen Roussel is its current director. A one-time criminal defence attorney who has been a government lawyer for much of her career, including in environmental law and the program that enforces gun-control rules, she was appointed in June 2017 for a term of seven years.

"The relationship between the attorney general and the director is premised on respect for the independence of the prosecution function and the need to consult on important matters of general interest," reads a news release announcing the appointment.

What does the justice minister have to do with it?

According to the legislation, the service's director acts under and on behalf of the attorney general, the Crown's chief lawyer, through whom it reports to Parliament.

In Canada, the same person is both justice minister and attorney general. Some other places, such as the United Kingdom, separate the justice minister's job from the attorney general's, though both positions are held by politicians.

Except for Canada Elections Act matters, the attorney general is allowed to direct or even personally take over prosecutions but must do so in writing and with notice published in the Canada Gazette, the official record of government decisions. For general prosecution directives, the attorney general must also consult with the director.

Does this happen a lot?

Not very often. But Wilson-Raybould used this power as recently as Nov. 30, with a direction in relation to HIV non-disclosure cases, telling federal prosecutors not to pursue charges against people with HIV who have sex without informing their partners, as long as the circumstances were such that there was virtually no chance of transmitting the illness.

The law didn't change but the instruction to federal prosecutors -- which only applied in the handful of jurisdictions where they handle criminal cases -- changed the way it is applied.