Wanted man Michael Cope, 28, has been arrested in Leigh, Greater Manchester, on suspicion of the murder of his ex-girlfriend Linzi Ashton, Press Association sources said.
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Members of the RMT on Arriva Rail North (Northern) walked out for 24 hours, with more stoppages due on Thursday and Saturday.
Police said a dozen shots were fired, but no arrests have been made and they are looking for a dark vehicle.
Former Conservative leader Lord Hague has called for "a major chance in policy" cannabis.