Canadian police say a suspect is in custody after at least four people - two of them police officers - were killed in a shooting in the eastern city of Fredericton, New Brunswick.

The slain officers were identified as Sarah Burns and Robb Costello, but the civilians - a man and a woman - have not been named.

The officers were responding to reports of shots fired when they were killed, officials told media.

Police have not mentioned a motive.

"Protecting us today, they gave their lives," Fredericton mayor Mike O'Brien told the media during a press conference. "We will get through this together but now my thoughts turn to the families of the victims."

Burns, 43, leaves behind a husband and three children, while Costello, 45, is survived by his partner and four children.

The following is a summary of the history of gun control laws in Canada:

The federal Parliament instituted a system of gun control in the North-West Territories in 1885 to hinder the Red River Rebellion for Métis rights. Permission in writing from the territorial government was needed to possess any firearm (other than a smooth-bore shotgun), and also ammunition. Possession of a firearm or ammunition without the necessary permit was an offence, and could lead to the forfeiture of the firearm and ammunition. These gun control provisions applied to all of what is now Alberta, Saskatchewan, parts of Manitoba, the current Northwest Territories, Yukon, and Nunavut.

The Criminal Code, enacted in 1892, required individuals to have a permit to carry a pistol unless the owner had cause to fear assault or injury. Not until 1935 was it considered an offence to sell a pistol to anyone under 16. Vendors who sold handguns had to keep records, including purchaser's name, the date of sale and a description of the gun.

In the 1920s, permits became necessary for all firearms newly acquired by foreigners.
Legislation in 1934 required the registration of handguns with records identifying the owner, the owner's address and the firearm. Registration certificates were issued and records kept by the Commissioner of the Royal Canadian Mounted Police (RCMP) or by other police forces designated by provincial attorneys general.

In 1947, the offence of "constructive murder" was added to the Criminal Code for offences resulting in death, when the offender carried a firearm. This offence was struck down as unconstitutional by the Supreme Court of Canada in a 1987 case called R. v. Vaillancourt.

Automatic firearms were added to the category of firearms that had to be registered in 1951. The registry system was centralized under the Commissioner of the RCMP.
In 1969, Bill C-150 created categories of "non-restricted", "restricted" and "prohibited" firearms. Police were also given preventive powers of search and seizure by judicial warrant if they had grounds to believe that firearms that belonged to an individual endangered the safety of society.

In 1977, Bill C-51 required firearms acquisition certificates (FACs) to purchase any firearm, and introduced controls on the selling of ammunition. Applicants were required to pass a basic criminal record check before receiving the FAC.

In 1991, Bill C-17 was introduced, coming into force between 1992 and 1994. It required FAC applicants to pass a safety course in addition to a thorough background check, and to wait a minimum of 28 days after applying before an FAC could be issued. It also created new Criminal Code offences, new definitions for prohibited and restricted weapons, and new regulations for firearms dealers. It increased penalties for firearm-related crimes. It clearly outlined regulations for firearms storage, handling and transportation.