Who instructs individuals not to cooperate with law enforcement investigations?
The law enforcement lobby, that’s who -
http://www.cleat.org/wp-content/uploads/2011/12/Garrity-Statement.pdf
“Who instructs individuals not to cooperate with law enforcement investigations?”
Nowhere in your link does it instruct anyone to NOT cooperate with law enforcement investigations.
In fact you link is an acknowledgement that the officer as part of his duty is to file an official report.