Webster Police Chief Gerald L. Pickering from New York State commenting on a gunman who killed two firefighters as they tackled a fire, said that it appeared that the gunman had "set a trap" for them.
He added that the gunman had died from a gunshot wound.
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Marjorie and Michael Cawdery, both 83, are understood to have been stabbed to death in a killing their family called "incomprehensible".
Detectives have launched a murder investigation following the shooting in Brent, north west London on Friday night.
Hot and humid throughout the Bank Holiday Weekend.