Hypo: Defendant turns himself in on a warrant and is in jail. Shortly afterwards, sheriff learns that a currency theft occurred in the lobby of the jail around the same time as defendant was seen there. Investigators go to see whether defendant saw anything and learn that defendant had currency in the amount that was stolen taken from defendant at booking. Defendant says the money was given to defendant to use for bail. When asked to provide a phone number of the donor to confirm the story, defendant cracks and admits the theft.

Is the unrecorded statement by a possible witness inadmissible if the witness was in custody at the time and later turns out to be the perpetrator? My sense is yes, but I'm hoping I missed something.

Article 38.22, based on Miranda, requires police to give a defendant Miranda warnings before taking a confession through custodial interrrogation. Texas law further restricts the admission of a confession to those that are written or recorded with warnings preceding the confession. Unrecorded oral confessions that result from custodial interrogation are admissible only if they result in the discovery of new evidence that incriminates the defendant.

So, if no Miranda warnings were given to a defendant who was in custody, regardless of the reason for the custody, any confession resulting from interrogation is likely to be inadmissible. The fact that a defendant was only jailed on unrelated charges does not change the fact that the defendant was in custody.

I had come to pretty much the same conclusion. I had hoped there was something similar to the offense-specific 6th Amendment assertion of rights, but it doesn't look like such a loophole exists in the Code.

Could you argue that the detectives were not interrogating a suspect (i.e. not asking questions reasonably likely to elicit an incriminating response), but rather simply investigating a possible witness? This probably became interrogation once the officers knew he had money in the missing amount, because he then became a suspect--but it might get you something.

Did he receive magistrate warnings between the time of his arrest and the time of his questioning? I am arguing that as a basis (among others) for admissibility of a similar statement, i.e. a detective trying to figure out what happened.