If there was no blood, what happened to the weegee blood on the shell?
Also, can Peach explain what happened when Mario got there, and why she was holding the shell?
SP4 seems an awful lot like SB4... as in Smash Bros. 4 3DS and Wii U. Perhaps Luigi's house is really Luigi's Mansion(as indicated by Mario's claim that Luigi needed help after catching King Boo again). And guess what? Luigi's Mansion is a stage in Smash Bros. Now, normally you kill an opponent by knocking them off the screen, but one mode changes that - specifically a Stamina battle. Super Mushrooms, Koopa Shells, Fire Flowers, and Bob-Ombs are all items in SSB, and you win Coins(or at least Gold) when you win a match. This "murder" could just be a stamina battle on the Luigi's Mansion stage in which Luigi was the first to lose his stamina. Also note that Luigi, Mario, and Peach are all SSB fighters, and there's one fighter who literally IS a black figure: Mr. Game & Watch.
http://objection.mrdictionary.net/go.php?n=8095979
Sure, I'll call her
Peach: Do you want me to add that to my testimony? Okay
Cross Examination
Peach:
Well, that day, Luigi had asked for my help to organize his house, so I went there at about 2 PM
When I arrived, he was sleeping on the couch, so I poked him a little bit until he woke up
I went to the kitchen to prepare my special 1-Up soup for him since he asked so nicely
Later, I heard a scream, so I went rushing back to the living room, and saw- I saw Luigi dead!
He was on the couch, and there was no blood or anything! But his pulse had stopped!
The newspaper on his hand had something written in red: SP4
I picked up the shell on the floor, and it was clean, like it was never used
Mario came in and was scared because I had the shell in my hands
After that, I called the police and when they arrived, I was arrested for "Being the only person at the crime scene"!
Oh, the nerve of those people! Arresting the princess like that! Without even evidence!
Testimony finished
One thing, defendant, may I ask a few questions?
Peach: W-What is it?
Why did you pick up the shell?
Peach: W-Well, b-because it was next to the dead body of course!
(she's definitely hiding something... I don't know if it's good or bad...A quick logic chess should do the trick)
HOLD IT!
Huh? Who said that?
Gumshoe: It was me, sir. We found something in the crime scene! We found... this!
What is that? It looks like an upside down GBA with an analog stick and 2 touch screens, "ATIV SP"... What ever this is, the letters are upside down, so it's pretty weird...