Police obtaining DNA samples by ruse (tricking a suspect into providing a saliva sample) does not necessarily constitute 'impropriety' under s 138 of the Evidence Act 1995, even where alternative lawful means of obtaining the sample existed but were not pursued. In cold cases relying on DNA evidence, a Longman/Crampton delay direction is not required where the delay did not prejudice the accused's ability to challenge the DNA evidence itself, as DNA does not change over time; the direction need only address prejudice to the accused's ability to establish an alibi or test other evidence.
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