I don't watch Corrie but I do know that the Old Bill treat any unexplained death as a possible crime until it can be proved otherwise.
For example, a few years ago the elderly lady who lived opposite me was found dead at the foot of her stairs. It was eventually decided that she'd either had a stroke, causing her to fall downstairs, or that she'd accidentally fallen downstairs, resulting in a stroke. In the meantime though the road was full of police cars, with plain-clothes officers carrying out door-to-door enquiries.
Similarly, every time someone jumps in front of a train (which is roughly once per day across the UK) British Transport Police always assume that they were pushed or, for example, that they were running away from an attacker, when the fatality occurred.
i.e. the rule used by the police is always "It's a crime scene unless we know otherwise".