So I'm asking this in the setting of a criminal trial, but I'd also be interested to hear about the treatment of the same aspect in a civil trial.
Assume Danny (D) finds himself accused of some wrongdoing. Maybe, to the layman, D is "the kind of guy who would to this kind of thing", but the primary reason comes from one Henry W (HW) - in front of the police, HW has testified that D has committed some crime.
HW told the police: "At dusk, I saw D sneak up to the back door of the factory building, carefully trying to stay in the shadows, open the door with some kind of tool, sneak inside; later, I saw him leave the building with a couple of expensive tools in his hands!"
However, unbeknownst to HW, D has been able to secure some unbiased, credible, and convincing evidence that exonerates him, or at least discredits the core of HW's claims.
D has been able to secure a copy of a CCTV camera that shows the back door in question - the pictures show him causally walk up to the open door, peek his head in, maybe yell "Anyone there? You guys know your back door is open?!", and, after waiting a short time, walk away through the lights of the street lamps, obviously empty-handed.
In the next court session, HW will be heard. It is to be expected that he will repeat what he said to the police.
D and his attorney can now act in a variety of ways:
- Try to preempt the hearing of HW, offering their evidence, so as to prevent HW to testify in a way that will cause him trouble.
- Wait out the hearing of HW, then offer their evidence, with HW now likely facing consequences for his untrue testimony.
- Wait out the hearing of HW, but cross-examine HW, giving him any opportunity to tell details which D knows aren't true, maybe more than what HW would have claimed in the previous option, and give HW any freedom to to embellish his story. Then, they request that HW be put under oath, leaving HW to face consequences of lying to court, worse than in the previous option, and while under oath.
What I'd like to know is: While option #2 is probably the most "neutral" way D and his attorney can go, is there any rule, formal or informal, that would compel them to lean towards option #1 or would forbid them to use option #3?
 I'm asking (also) for Germany, where witnesses are only put under oath on request by either side after testimony