Kate McCann, whose daughter Madeleine was abducted in Portugal in 2007, says she has not been put off competing in the London marathon by the Boston bombings.
She is an ambassador of the Missing People charity and is aiming to raise £20,000 to mark its 20th anniversary.
"This sickening act is just incomprehensible and the loss of life, especially that of a young child, heart-breaking.
"But I feel strongly that you can't live in fear or you don't have a life."
More top news
Cloud will thicken with some, mainly light, patchy rain possible through this afternoon and into tonight, with some clear spells.
This morning's sunny spells will gradually give way to cloudier, breezier conditions this afternoon, with patchy rain possible later.
Former Aston Villa legend Stiliyan Petrov, who battled leukaemia last year, has kitted out every player in his new Sunday soccer side.