Two boys aged 14 and 15 are still being questioned by police investigating the murder of an 85-year-old woman in Greenford.
Paula Castle was mugged in an alleyway beside a primary school on Monday afternoon.
She died in hospital the following day.
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Police arrived at the 73-year-old's home after Alfie chased a delivery man.
Officers believe the three assaults are linked and are appealing for information about the suspect.
Nine addresses in Lewisham were searched and 13 arrests made early on Tuesday morning in a planned, intelligence-led operation.