Crufts organiser the Kennel Club is trying to contact the owners of six dogs that could have been poisoned at the competition.
The organisation is attempting to track down the owners of two Shetland sheepdogs, a West Highland White terrier, an Afghan hound and a Shih Tzu.
The search comes after three-year-old Irish Setter Thendara Satisfaction, known as Jagger, died after returning home to Belgium after finishing second in his class at the show at Birmingham's NEC on 5 March.
One theory is the killer of Jagger also targeted the six other dogs. The Kennel Club said it was aware of the reports of six poisonings and was investigating the claims.
A Shetland sheepdog is thought to have been poisoned the day after the Irish setter and the incident has sparked suggestions that dogs may have been poisoned at the event in previous years.
The allegation was refuted by Kennel Club, which said it had never received reports of dogs being poisoned at the showpiece event before.
Reacting to the news Jagger had died, Kennel Club secretary Caroline Kisko said: "We are deeply shocked and saddened to hear of Jagger's death and our heartfelt sympathies go out to his owners.
"Whilst we are unclear of exactly what happened, we understand that a toxicology report is due next week and that this matter has been reported to the police – we will work with them and help however we can. We are in contact with the owners and will do all we can to support them at this sad time."
Jagger's owner claimed three types of poison had been found in beef, including what appeared to be slug pellets and rat poison. Belgian police are also looking into the death and are scouring CCTV to find the culprit.