We don't trust in-custody inmate testimony because (inter alia) we're concerned -- for good and empirical reasons -- that inmates might lie and incriminate another prisoner to get a reduced sentence in their own case.
We don't trust accomplice testimony for identical reasons.
As a result, in California, you've got to have corroboration. You can't convict someone based on only the testimony of a "jailhouse informant". Penal Code Section 1111.5. Ditto for accomplice testimony. Penal Code 1111.
Imagine a case where you've got no objective corroboration. But you have both accomplice and jailhouse informant testimony.
Is that enough? Do two presumptively unreliable pieces of information combine to create information that is now reliable?
The Court of Appeal says "Yes."
I know that some of you may be thinking that this is another April Fool's joke. But it's not. That's actually the Court of Appeal's holding.