How did she know?

On a crisp fall day, Ms. Dunnit's old friend Purl was planting a border of Tulip bulbs around her garden. She was very proud of her gardens but she knew that this was probably the last year she would be able to do the planting herself. She had suffered two heart attacks in the past year and her doctor had warned her that she would not survive another. It was late in the afternoon when she finally began the last row of planting. Suddenly a shadow fell across the flowerbed and she heard a voice say "Hello, Auntie". It was her good for nothing nephew, Tink, who was always begging for money. But, not this time - this time he announced that he had come to kill her! He knew, that although she had bequeathed her house and gardens to a museum with the stipulation that they keep them exactly as she had left them, the rest of her estate would be his. Tink had gambling debts that needed to be paid off and he had decided he could not wait for his aunt to die of natural causes.

Not knowing what else to do, Aunt Purl went on planting her tulip bulbs very carefully. Whatever happened she was determined to finish planting the garden. Suddenly she turned and saw Tink take something out of his pocket. It was a water pistol and he explained that it contained Amyl nitrate, which was a powerful heart stimulant. He began squirting her with it, knowing that it would cause a fatal heart attack and that by the time her body was found the rain that was predicted for later that day, would have washed all traces of the amyl nitrate away.

When Ms. Dunnit called to pay a visit the next day, she found Purl's corpse in the garden and called the police. The coroner ruled death by natural causes and no one (except Ms. Dunnit) saw any reason to doubt it. Tink inherited the bulk of her estate, except for the house and gardens, and promptly began squandering it on gambling and other unsavory activities.

In the spring Ms. Dunnit paid a visit to the police and told them she knew that her friend Purl had been murdered and she knew who did it!

How did Ms. Dunnit know that Tink had killed her friend?

E-mail your answers to me at grammieknits@yahoo.com (please don't comment on the blog - you'll give it away!) by Saturday, May 17.