Chief Superintendent Steve Neill says officers would like to hear from people who may have seen anything unusual in Stanley Street at any time in the last few days.
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Nigel Farage's former deputy Mr Nuttall says he's the only candidate who can rebuild and unify the party.
The 27-year-old was stabbed in Arthur's Hill, Newcastle on Monday and later died in hospital.
Newcastle get three points from the match and now three points clear at the top.