What is the current state of the law on "interrogation" in criminal proceedings?

This is incorrect. Settled law shows that Jefferson and Staten were not "interrogated." "Interrogation" requires "a measure of compulsion above and beyond that inherent in custody itself." (Rhode Island v. Innis, supra, 446 U.S. at p. 300, 100 S.Ct. 1682.) That compulsion is missing when a suspect speaks freely to someone the suspect thinks is a fellow cellmate. "When a suspect considers himself in the company of cellmates and not officers, the coercive atmosphere is lacking." (Illinois v. Perkins (1990) 496 U.S. 292, 296, 300, 110 S.Ct. 2394, 110 L.Ed.2d 243 [undercover law enforcement officer posing as a fellow inmate need not provide Miranda warnings before asking questions likely to elicit an incriminating response];

[70 Cal.Rptr.3d 459]