Locals are saying the attack centered on a butcher shop in Grosvenor Road, which is very well known and is one of Rotherham's oldest family businesses.
Lots of car windows have been smashed on Grosvenor Road.
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The 10K and half-marathon races take place almost exactly a year after Salman Abedi killed 22 in his attack at an Ariana Grande concert.
Dmitrios Pagourtzis also had several kinds of homemade explosive devices but they were not capable of detonating, county officials said.
After early mist clears, most parts of England and Wales will have another fine, warm day with plenty of sunshine.