In a case shrouded in many mysteries, one of the biggest is how Oscar Pistorius obtained a licence for the 9-millimetre semi-automatic pistol that killed his girlfriend.

Gun-control advocates say the Olympic hero should have been denied a licence for the handgun when he applied in 2010 because he had already spent a night in jail for allegedly assaulting a woman at a party a year earlier.

Even after the handgun licence was issued, they say, it should have been later revoked because of his involvement in other incidents, including an alleged threat to break another man's legs in November and an accidental gunshot at a restaurant in an upscale Johannesburg shopping mall in January.

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Mr. Pistorius was denied a gun licence when he first applied in 2008 – the reasons were not disclosed. But he appealed the decision and was granted a licence in 2010.

The fact that Mr. Pistorius still had possession of his pistol last week, and used it to kill Reeva Steenkamp, shows that lax enforcement is jeopardizing South Africa's strict firearms laws, activists say.

In many ways, South Africa's gun laws have been a model for the world. Evidence strongly suggests that they have sharply reduced the rate of firearms-related homicides in the country since 2004 when they took effect. The level of gun-related crime has dropped by 21 per cent since 2004, and a study of female victims found a dramatic decline in murders caused by guns from 1999 to 2009.

Yet those laws are increasingly undermined by corruption and loose enforcement among South African police and government officials. In one case last year, a pair of confessed killers were able to obtain licences for nine firearms.

Mikey Schultz and Nigel McGurk, two underworld figures with long histories of violence who confessed to the shooting of mining tycoon Brett Kebble in 2005, were mysteriously granted licences for nine guns last year, according to a report in Johannesburg's Star newspaper.

In another case, reported three weeks ago, a senior police officer resigned from his post at a Johannesburg police station after an investigation was launched into allegations that he issued gun licences to a businessman in exchange for cash. The police officer was a former official at the South Africa's central firearms registry.

South Africa's gun-control laws were the product of public debates in the late 1990s, when the country was revising its apartheid-era laws after the birth of democracy in 1994. Six weeks of public hearings were held, and many gun owners lobbied vigorously against the reforms. "It was a huge battle," recalls Adele Kirsten, a gun-control activist who has written a book about the period.

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The new law took effect in 2004, and gun owners turned in more than 100,000 firearms in a national amnesty program.

The gun-control policy, one of the toughest in the world, created a two-step process for getting a gun licence. Before applying for the licence, a would-be owner must obtain a "competency certificate," including a gun-safety test and background checks to see if the applicant has a history of violence, addiction or other issues.

Even if the applicant does not have a criminal record, a licence can still be denied if the person was "visited by a police official concerning allegations of violence in the applicant's home" or if the applicant "has been reported to the police or social services for alleged threatened or attempted violence or other conflict in the applicant's home or elsewhere," the regulations say.

Because of those rules, it is unclear why Mr. Pistorius was given a gun licence.

He was never charged for the alleged assault in 2009, and he is suing the woman who filed the complaint against him. But regardless of whether he was charged, the incident should have been enough to prevent him from getting a gun licence, according to Ms. Kirsten and other gun-control activists.

Last month, according to several media reports, Mr. Pistorius applied for licences for six more guns, including a long-range Vector .223 rifle whose bullets can travel for up to a kilometre, and a Smith & Wesson Model 500 revolver that is described as "the world's most powerful handgun."

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At the bail hearing this week, an investigator said the police are planning to charge Mr. Pistorius with a firearms offence because they found unregistered .38 calibre ammunition in a safe in his home after he shot his girlfriend.

Mr. Pistorius has said that he goes to shooting ranges "when I can't sleep." He once boasted on Twitter that he had a "96% headshot over 300m from 50 shots" at a shooting range. "Bam!" he added.