Harrow is lucky to be a borough that doesn't see many murders. And those that it does, like that of pensioner Molly Morgan, seem genuinely isolated incidents.
Although worrying, they don't leave an air of foreboding that retaliation is on the way.
But those were exactly the rumours circulating the borough after the death of 19-yearold Hassan Kul-Hawadleh.
Reports of some kind of feud, possibly between the borough's Somali and Afghan communities were allowed to run unchecked since the killing on Thursday.
The public understands that detectives are limited in what they can say while an investigation is going on, but appeals for calm should have been made earlier by the borough's police and the Somali/Afghan rumour quashed sooner. Schools and youth groups should have been informed immediately and reassurances offered.
Borough commander Richard Walton has since denied that any kind of animosity exists between the groups but some young people believe differently.
And in the absence of much other information about why this would happen between two apparent strangers - one of whom seemed to be simply passing through - dangerous speculation among the young will surely flourish.
Police have brought in emergency powers of the kind used when serious violence is expected; they can now search anyone in the area of the killing at will. The public is left mystified.
With luck the killer will be brought to justice and in an open court the reasons for this shocking death will be made clear.
For the time being Harrow must unite in its shock that something like this could happen and do the right thing in staying calm and co-operating with the detectives.