I don't think Ago said that.
Bach said "I don't think that he needs to specify for the defense exactly how we have confirmed that they're (sic) Winfield defendant if that's what he is, is not truly a Winfield defendant."
Then later Ago backs up from trying to portray JW as a viable alternative defendant and says he's just trying to establish JW's credibility, or lack thereof: "W-1 is a crucial witness in this case, Your Honor, and if we can -- there are statements that W-1's made to the police, and what we are trying to do is explore W-1's credibility. And I think we're allowed to do that. It's not a Winfield -- we're not --"
Sounds like Ago was fishing for information, floating JW out there as coming into the house to commit the murders after DW left after his pizza dinner, but once he got called on that, he switched to discrediting JW as a witness. Doesn't the prosecution have to turn over evidence that confirms JW's whereabouts during the crime, or no? Why the fishing expedition if the defense will receive all this information anyway? Legal Eagles? Help?