The first thing that should be investigated at crime scenes is law enforcement.
There are virtual no independent monitors at crime scenes. This gives law enforcement far too much power and the ability to push any narrative they want.
The FBI has the power to withhold evidence from the state, county, and local law enforcement at crime scenes.
The public can no longer be naive about this matter.
The False Promise of DNA Testing
https://en.wikipedia.org/wiki/False_evidence
https://www.forensicscolleges.com/blog/resources/real-cases-of-forensic-fraud-flawed-evidence
https://en.wikipedia.org/wiki/Internal_affairs_(law_enforcement)