Am not condoning any wrong-doing, this extract from an article by Matthew T. Martens [an eminent US based trial lawyer, ex-Federal Prosecutor, ex-Defense Attorney] is food for thought.
The conundrum of wrongful conviction has stalked mankind from the earliest of ages. Irenaeus of Lyon (AD c. 130–c. 202), in his influential work Against Heresies, recognizes the authority of magistrates to bear the sword and also implies that “whatsoever they [the magistrates] do to the subversion of justice, iniquitously, and illegally, and tyrannically, in these things shall they also perish".
If a criminal justice system is designed and operated so that it takes all reasonable means to avoid wrongful convictions, then a government official (whether judge, prosecutor, or police officer) who participates in that system is not a wrongdoer even if that system results in a wrongful conviction. For the most part, “just following the law” will be a defense that absolutely precludes criminal prosecution of a government official.
The police are protected by a qualified immunity that is nearly absolute.
[Pierson v. Ray, 386 U.S. 547, 557 (1967) qualified police immunity]
The person wrongfully convicted in that situation has most certainly suffered an injustice, thankfully this has not happened in this case being discussed.
[Yes, the US justice system is not the same as the commonwealth's, but the occurrence of possible wrongful conviction happens in both jurisdictions]