What tunnel vision is,
and what it leaves in the file.

Tunnel vision describes a way of working a case, not a state of mind. It occurs when an investigation settles on a suspect or a theory early, and the work that follows narrows to support that choice. Leads that confirm the theory get pursued, corroborated and written into the case narrative. Leads that would undercut it get noted once, deferred, or never worked at all. None of that requires bad faith, and a practices analysis does not assume any. What it examines is the sequence of investigative decisions and whether each one was supported by the information the investigator actually held at the time.

The distinction that matters in review is between focus and premature commitment. Every investigation narrows eventually; that is what a solved case looks like. The question is whether the narrowing followed the evidence or preceded it. An investigation that runs alternatives down, documents the results and then concentrates its resources has focused. An investigation that concentrates first and documents nothing about the alternatives has committed, and the file shows the difference.

The two directions evidence gets filtered.

• Confirming information is collected, corroborated and carried forward into later reports
• Disconfirming information is logged in a supplement and left there without follow-up
• Interviews are built around the theory rather than around what the witness can independently supply
• Evidence collection becomes selective, matched to the account already in hand
• Alternative suspects are set aside with no documented basis for eliminating them
• Successive reports restate the early conclusion rather than test it

In post-conviction and wrongful conviction review, tunnel vision is rarely the claim itself. It is the explanation for a set of concrete omissions counsel intends to prove: the witness never interviewed, the alternative suspect never cleared, the item collected but never submitted. The value of a practices analysis is that it converts a pattern into particulars, each one anchored to a document or to the documented absence of one.

The analysis runs the same way for counsel defending an agency. Where the file shows that alternatives were worked and closed on paper, that canvass leads were returned, and that the narrowing followed the evidence, the report says exactly that. That finding carries weight because the same method produces the opposite finding when the record requires it.

Custody and handling questions travel with these reviews, since an item collected and never tracked reads much like an item never collected; that subject is covered in what chain of custody requires. Where scientific, medical or technical questions arise, qualified experts in those disciplines are deferred to on the record. And the ultimate questions, including whether a disclosure obligation was breached under Brady v. Maryland, 373 U.S. 83 (1963), and what relief should follow, are legal conclusions that remain counsel’s. The expert addresses police practices.