I don't know how it is in the UK, but in the US cops are NOT required to look at exculpatory evidence before they arrest you. Their job is to gather evidence that leads to an arrest and any evidence they look at that gives them probable cause is the only thing they are required to consider for the arrest.

In fact once they arrest you their job is over... there is no obligation to look at every possible scenario and find more evidence either of your guilt or innocence. Even if people tell them there is evidence of their innocence, US cops are not required to look at it and can just straight up ignore it. Shows like CSI where they look into every alibi and piece of evidnce is a complete farce. Their modus operendi is "Let the Judge sort it out."

You can see this in practice with the lady who came out of the restaurant and found her car windshield smashed in. She call the cops and the cops knew there was a recent hit and run so they assumed she was driving while intoxicated and made up the story to get out of trouble. They arrested her for DUI and hit and run etc etc. She told them to ask in side the restaurant and get teh security footage ass it would show she was parked here for 2+ hours and inside the restaurant so the hit and run couldn't possibly be her. Cops didn't care. Her own lawyer had to get the footage themselves to prove her innocence, the cops never bothered to look into the matter further after arresting her.

And when she sued, the judges didn't care and said essentially what I posted above: Cops are not required to gather ALL evidence possible nor any evidence that proves your innocence even if told about it's existence. Once they have probable cause to arrest, their job is over and done. So she lost her lawsuit.

Hurray for America!! There is no Justice in our Justice system>.<