We've got a robbery defendant who's committed a lot of extraneous acts, mostly robberies. A couple of years ago, he robbed a convenience store, but that case was unsolved until he robbed another local convenience store months later. In the process, he threw a brick, which remained in the store with his DNA on it. Swabbed, submitted, CODIS hit, evidentiary SW, buccal swabs, DNA comparison, bingo.

How do I try robbery #1 without putting on evidence of robbery #2 (i.e. the brick)?

Unless I'm misunderstanding your question, I don't think this is a situation where you have to.

"The rules of evidence are intended to let evidence in, not keep it out." De La Paz v. State, 279 S.W.3d 336, 343 (Tex. Crim. App. 2009).

The Court of Criminal Appeals has established that evidence of extraneous offenses is admissible when the offense or transaction is 1) relevant to a material issue in the case and 2) its probative value outweighs its inflammatory nature. Parks v. State, 746 S.W.2d 738, 740 (Tex. Crim. App. 1987); Page v. State,213 S.W. 3d 332, 336 (Tex. Crim. App. 2006).

It's late on a Friday, so maybe I'm missing what you're getting at, but I think you're on solid ground.

There's probably not enough similarities between the 2 robberies to make robbery #2 admissible as to identity/signature crime under Page. But without the brick (robbery #2) there's no arrest in robbery #1.

This seems like res gestae (Parks) i.e. "events don't occur in a vaccum". The brick established PC for robbery #2, which led to a confession in robberies 1-7. The defendant's having buyer's remorse.

Don't ask about the source of the comparison print. Just refer to it before the jury as a print supplied by the defendant or some such.