BBC Northern Ireland (NI) Spotlight reporter Mandy McAuley, whose story The Pit Bull Sting won the Royal Television Society awards' nations and regions current affairs category this year, explains how it was done.

It was a tip off from an animal welfare charity almost two years ago that started our investigation into the world of organised dog fighting.

The USPCA (Ulster Society for the Prevention of Cruelty to Animals) had intelligence that a top-class fighting dog was en route from Frankfurt to Dublin. Within 24 hours, they had tracked the dog from Dublin airport to Co Tyrone and the home of one of NI's best-known sporting heroes, Ger Cavlan.

And the most significant find was a stash of match reports. They read like a who's who of the international dog-fighting community. Almost all of the top fighting gangs in Ireland and Britain were listed.

We had long wanted to blow apart the savage and secret world of dog fighting. Now we had enough intelligence to infiltrate it.

We enlisted the help of a trained undercover operative - "Steve" a former soldier who had already worked with dangerous dogs.

The passport for the dog seized from Cavlan's house told us it was Cannon Ball. It was a 100 per cent pure pit bull and had injuries consistent with dog fighting.

The next lead was an advertising brochure, found at Cavlan's house, for a pit bull supplier based near Helsinki, called Dunkel kennels.

Weeks later, we arrived in Helsinki, posing as dog fighters eager to buy a top-class pit bull to smuggle back to NI. We found the kennels in remote woods on the outskirts of the city. As Paul Dunkel and his wife showed us around their kennels, we secretly filmed more than 40 dogs tethered to trees. It became clear that we were standing in a dog-fighting factory.

A pit bull called Nipper could be ours for 2000 euros. Months later, we successfully smuggled Nipper into NI.

In the meantime, we hoped our newly acquired Finnish connections would help us break into the dog-fighting network in NI. One of the leading gangs, the Farmers Boys, was based in County Armagh. "Steve" spotted the head of the gang at a local dog show and started talking to him about our recent visit to Dunkel kennels. Having convinced him of his dog-fighting credentials, "Steve" got an invitation to a local pub where the dog fighters often drank.

"Steve" would become a regular visitor there. Unaware he was being filmed, the head of the Farmers Boys boasted about the number of champion pit bulls he had bred and exported. We had successfully infiltrated a gang of major players.

After a number of months, Steve flew to Finland with gang members to attend a series of dog fights at the kennels of Bobby Gonzales, the man named on Cannon Ball's pet passport. Men from Finland, Holland, Sweden and the UK were there. We had secret cameras trained on the ring, giving us the crucial film evidence we needed to expose the network behind the so-called sport.

As the night progressed, the ring became saturated with blood as dogs as young as eight months squared up to each other. We returned to Finland to confront Gonzales and the Dunkels and to hand our evidence over to Finnish police. The Farmers Boys have now disbanded.

Ger Cavlan, a Tyrone GAA football player, was fined £650 and banned for five years from owning a terrier-type dog after pleading guilty to possession of a dangerous dog.