Feed the birds

A journalist sat on a bench in Hyde Park where an old lady was feeding the pigeons and they struck up a conversation. She told him she fed the birds there everyday, always arriving at 11am. He warmed to her and he found her again at the same time the following day. She told him a little of her life. He liked her even more.
The following week, he was passing by and went to see her but she wasn't there. He went there again the next day but there was no sign of her, nor the day after. He asked a park attendant if he knew of the old lady who fed the birds. "Oh yes," the attendant said. "She arrives at 11am and leaves at 11.45 to take the 58 bus."
The journalist went to the bus stop at 11.45. The 58 arrived and he asked the driver if he knew of an old lady who usually caught the bus at that time. "I'm a temporary driver on this route," the man replied. "The usual driver will be back in a couple of days."
Two days later, the journalist asked the same question to the bus driver. "Yes I know her," he said. "She gets off at Notting Hill. I can show you her stop if you like?"
The journalist alighted in Notting Hill. There was a newspaper stand on the street. He asked the paper seller if he knew the old lady. "Oh yes!" he said. "She lives three streets down on the left, in the first mansion block on the right. Don't know which flat she's in though."
The journalist found the mansion block and asked the concierge where he might find the old lady who fed the birds in Hyde Park. "You've missed her," the concierge replied. "She died last week. She kept two large jars in the kitchen, one containing sugar and the other arsenic and she mistook the one for the other. She used to take the arsenic everyday to the park to feed the pigeons."