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."
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Lawyers representing the Birmingham pub bombings families are continuing to push for Hillsborough-style funding for the forthcoming inquest.
Police investigating the death of 50-year-old grandad David Lamont from Coventry have arrested a man on suspicion of murder.
A family were forced to pull over on the M5 in Worcestershire after their child found a 5ft snake in their car.