A crime scene examiner's visual observation of apparent blood staining, where laboratory testing fails to confirm the substance is blood, may have insufficient probative value to survive a s 137 challenge, particularly where there is a real risk of jury speculation. By contrast, DNA evidence linking an accused to implements used in a crime, supported by expert opinion on direct transference, is plainly relevant and its probative value is not readily outweighed by the danger of unfair prejudice, especially where the limitations of the expert evidence can be tested through cross-examination.
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