Well, thanks to you Enthalpy for playing through all the case especially with your difficulties. I was hoping I was not too insisting on that (I can't recall the number of bumps I made ^^), and so it's at least a good thing that you enjoyed the case.
About the english, well, I did my best but as non-native english speaker, I could not make a perfect translation, so I'll make a request soon enough for a complete check. Thank you for the first few things you pointed out by the way.
About the case logic, I read your post about it and it's very interesting. I did not searched the difference between the two flows, nor I tried to use one particularly. I can give you a global explanation of how I thought about that case (but as it's two-years old, I may have forgotten some things...).
First, it was during the contest of the Bright Age of the Law, during which there was also a character contest. I created Leviath for both of them, as I wanted a character who wanted to take everything on his shoulder, trying to fight the Dark Age alone. So I settled on someone with a strong morality but also much pride : as such, he would not be an opponent trying to bring down the defense by all means. So the opposition needed to come from somewhere else.
Then I thought about the Dark Age itself : during Dual Destinies, what we saw about that dark age was essentially the justice's side. So I wanted to make some mundane people affected by those events : a killer set free because of the manipulation of an amoral attorney, and a family trying to take revenge on him. I had pretty much the point of the second trial. However, I felt like it needed an introduction for most of the characters : that gave me the opportunity to unravel the persona of Leviath and Andrew, as well as presenting Silipee and his strangeness before his death. I had some ideas for a stand alone case before the contest, involing someone getting thrown out a window : it gave me the murder of the first case. I then worked a motive, what brought Silipee at that place and the rest came more or less naturally.
This is for the story. The logic of the gameplay came after that, and sometimes during the writing of the case.
For the first murder, I used the bases I had, and created all of the elements used during the murder (the tablecloth, the scissors, the lock and the map) and I tried to find all the points who could be used by the defense to progress. When I found a contradiction that could not be resolved by a handwave, I added something to make it work : the best example is probably the walkman, which was added to explain why Silipee did not heard any ruckus. Once I had the most of the useful evidences, I worked on the testimonies.
When I created them, I kept in mind that Leviath had a problem with the initial theory but didn't found something that could satisfy his doubt. Then I had the idea of the theory development (as you said ^^) : to advance his own theories, Leviath asks Phoenix about what HE thinks about that case, without a need for evidence at first. The goal was triple : make the story progress without a cross-examination or absolute evidence, use a new gameplay (I really like in general a little mechanic for a breath of fresh air) and finally verify what the player understood about the case. Leviath's character offered the possibility of such a mechanic, as he's motivated by the truth more than a win. However, as he was put in the prosecution's place against his will for the first case, he was a little more unwilling to help the defense.
Finally, the twist I wanted to incorporate was that the "last witness" to take the stand was not the true culprit : so I made Tiara appear early, and the trial first followed a wrong way toward Andrew. When Phoenix finally goes back on track and try to incriminate Tiara, the opposition Leviath could represent switch to her. And when she's defeated, there are still some loose ends that are supposed to appear in the next part.
The second murder was harder to create : I had to start from scratch, and the deadline for the contest was approaching. I don't really remember why I chose that crime scene in particular, and I recall trying to make a crime scene's photo, but I did not had the time so I had to find other ways to circumvent this. That said, I knew how I wanted to make the case happen : the case was suspicious and foggy enough to make both Phoenix and Leviath want to investigate the matter in court. Leviath is way more sure of his stand than before, yet he knows that Phoenix is not an amoral attorney. He has less holes in his initial theory because he's partly right, and yet I had to make another truth to discover : Leviath doesn't have all the cards in hand, and as the trial progress, some discrepancy appear for him : that's why he works more with Phoenix for the final part, when Xavier takes the stand.
The last theory development was not incorporated in the contest's version because I did not had the time to finish properly. I included it after as people told me the end seemed a bit bland.
So globally, I'm note sure if that style of writing is good, or if I tend toward a specific flow or another, but I try to have consistency in general, as loose ends often feel a little annoying for me (both as a player and as an author). I would gladly talk more about it or listen to some advices if you want !