A 26-year-old man remains in custody after he was arrested on suspicion of the murder of 84-year-old Louisa Denby, who he is related to, and the attempted murder of a nine-year-old boy who was stabbed in a skate park, police said.
A second 26-year-old man was also arrested in connection with Mrs Denby's murder, while three men aged 18, 24 and 29 were held on suspicion of attempted murder over the incident in the skate park.
All four have been released without charge, police said.
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Jonathan Theobald said: "The weather can change quickly and a car can become lethal, I've discovered that the hard way."
Political parties across the country suspended their General Election campaigns following the Manchester Arena terror attack on Monday.