AOG,
Just taking one short period when there was one more murder in London than there was in New York, does not prove an overall trend. It is being reported because it is unusual not because it is usual.
I could take a day with an unusually high death rate in New York, 11th September 2001 for example, when 2,996 people were murdered in a single day. Comparing that day in New York to that day in London would be stupid, as is your comparison.