By Clayton T. Robertson (Criminal Defense / Civil Litigation Attorney)
Law enforcement's failure to adequately investigate an alleged crime can be used effectively at trial as part of a reasonable doubt defense.
This constitutes one of my favorite themes: Prosecute the prosecution.
In other words, turn the trial around on them -- use "law and order" themes against the prosecution (and, in the process, appeal to those juror types) by showing breaches of their values (e.g., apprehending the guilty, following and playing by the rules, doing the right thing, protecting society, etc.).
Civil attorneys likewise do this through a technique called "negative spacing" -- i.e., examining everything that was NOT done (by an expert, deponent, etc.) and focusing the jury's attention on those issues. This same technique can be used in criminal cases and trials.
In both a civil litigation and criminal defense setting, this is not a red herring strategy. In fact, it's a credible way to show how what was not done affects the credibility and reliability of the results.
Finally, in any given case, this strategy may be buttressed by experts who testify about the consequences of "confirmation bias" and how law enforcement collects only just enough data points to land on an initial target/suspect without a thorough exploration of innocence or evaluating other suspects.