A family liaison officer has read out a statement on behalf of Craig De la Haye - a Jersey man whose wife Marta and five-year-old daughter Julia were both killed by Damian Rzeszowski.
They were both visiting the property where the Rzeszowskis lived when Damian turned on his own family.
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.