evidential

The watchdog said this "made it impossible to assess the evidential value of the information" but said a new process had since been agreed to share evidence.

Only four of the 12 people arrested met the evidential threshold to bring charges, according to the Crown Prosecution Service.

The force added that it had been a "complex investigation" and all "evidential opportunities" had been explored.

Mrs Anderson said they should have been kept by the police "for evidential purposes in respect of unsolved murders, including Mr O'Hara's".

It also acknowledges that the current legislation is too severe and has provisionally proposed that claimants could still be asked to prove their innocence, but be expected to meet a lower evidential threshold.