Very well.

Isumi comitted suicide under the threat of Kenny murdering his wife! Arn was murdered at the same time Isumi shot the gun!

<Good>!

Rinne is an accomplice as well! she was the one who shot Isumi while Kenny shot Arn!

The bullet that killed Isumi penetrated his body and grazed Arn, resulting in him receiving a bleeding wound, Kenny merely left through the window, grabbed the bullet and replaced it inside the body, alternatively he just placed a smashed bullet inside Isumi's head after the bullet broke the window and harmed Arn.

From there Arn bled to death, either from the bullet wound or the glass shards, and was dragged to the basement and had his torso destroyed.

This creates no contradictions since both deaths were generated from the gun.

While it's true that No lineup shot. has been said in red.

That would only apply to both of them dying from the bullet instantly.

Not done yet!

The gun that killed Arn and blasted the window was different from the gun that killed Isumi, resulting in a quieter bang that wasn't heard by Minchir!

....

Isumi was truly shot by Kenny's gun, however the noise that Minchir heard did not come from the gunshot that caused Isumi's death, it came from the gunshot that caused Arn's death.

Isumi's house is relatively soundproof to the point that as long as it's perfectly closed a gunshot wouldn't be heard from the Brother's house.

Useless.

Same theory, but with the following revisions:

Kenny murders Isumi from the inside, and placed a smashed bullet inside the disfigured head.

Arn witnessed the murder from the outside, which prompted Kenny to shoot him from the window, from there he drags his body to Arn's basement. And destroys his torso to erase the bullet wound.

His master key and pendant were stolen at this point. Furthermore the bloody snow was caused by Arn's body.

By the time Noah collapsed both Arn and Isumi were dead, Kenny disguises himself as the ghost and gives Nora the pendant, drags Noah's body outside and stabs it to guarantee his death.

As for how Kenny got inside the Couple's house:

Method #1: he knocked and was let in by Isumi under the pretense of wanting to talk.

Method #2: he stole Arn's master key during the dinner party and entered with it, which could lead to Arn being in the window since he would likely wish to use Isumi's key to go home.

Kenny culprit theory, with Noah accomplice.

Before Isumi was killed, Kenny and Noah switched clothes to switch identities, this is possible because they are identical twins.

From there Noah dressed as Kenny accompanied Nora and Solene to their house and kept Nora company when Solene returned, meanwhile Kenny dressed as Noah intercepts Arn when he's entering his house and incapacitates him, stealing his pendant and key, and placing him in the basement, either setting up a delayed kill mechanism by hooking him up to the generator in a way that would explode his torso, or killing him after Isumi died by sprinting to his house and comitting the crime.

Noah as the accomplice proceeds to trigger a gas leak from the inside by letting carbon monoxide from the heater system loose. Poisoning both of them.

From there two possibilities exist:

Scenario #1: Noah threatens Nora to murder Solene if she doesn't collaborate and lie about him collapsing and seeing the ghost, from there Kenny arrives and gives her the pendant.

Scenario #2: Noah dressed as Kenny truly collapses and Kenny disguised as the ghost arrives, gives Nora the pendant and drags Noah outside.

From there Kenny uses Arn's master key, unlocks the Couple's house door and shoots Isumi in the head from either the door entrance or the outside, the impact knocked Isumi's corpse towards the window, breaking it. The door is then locked from the outside.

It is true that The window was pretty much destroyed by a gunshot, However it's possible that it's a simple wordplay trick, the gunshot indirectly caused the damaged window, therefore no contradictions exist.

After killing Isumi, Kenny swiftly stabbed Noah's corpse and buried it near the Couple's house his leaking blood reddening the snow. Noah was already dead shortly after Isumi's death, from a combination of freezing temperatures and carbon monoxide poisoning.

All other murders were trivial.

Solene culprit theory, with Kenny as the accomplice.

Arn and Noah were the first victims, Arn was incapacitated when he was entering his house and was then murdered by Kenny in the basement, from there Kenny took his master key and his pendant.

Noah was murdered shortly after, his body left buried in snow.

Solene was accompanied by Kenny to put Nora to sleep, Solene never actually entered the house, she merely left Nora with Kenny and said she was going back, in actuality she was putting on her disguise and either pumping poison gas into her house or triggering some form of gas leak.

Solene then enters the house after Nora and Kenny are poisoned.

Kenny faked his collapse. After Solene gave Arn's pendant to Nora she moved his body elsewhere while Nora cowered in fear, from there Kenny moved to the couple's house.

Isumi's murder was the last one prior to the discovery of the bodies. He was shot by Kenny through the Couple's house window from the outside, with the bullet impact splattering blood outside. This is possible because Isumi was near the door before his death.

The remaining murders where trivially done by Solene killing the remaining victims and moving the bodies.

The culprit is Arn, his accomplice is Noah.

Before faking his death, he poisoned Kenny, this was done through lacing his pendant with poison, and having him inspect it at any point prior to his collapse with Nora.

Arn's death was faked, the "body" seen by the detective was actually a sculpture covered in blood and animal meat. After faking his death he dressed himself as the ghost, from there he gave Noah the gun and ordered him to shoot Isumi from the Couple's window.

Revision: the shot was done from the outside, and the bullet impact splattered the blood from the victim's head to the outside snow. This is possible because Isumi was near the window at the time of the shot.

The poison that killed Nora was naturally the one from the pendant.

After killing Isumi, Noah regrouped with Arn and both of them carried out the remaining murders by entering the relevant houses with Arn's master key and moving the corpses.

Dlanor swiftly leaped to the heavens to meet Erika midway through her ascent.

As she reached Erika she mercilessly struck her with her dual swords, finally ending the fight with a finishing move.

"This fight is officially FINISHED. FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED, FINISHED.

<Die the death>!

<Sentence to death>!

<Great equalizer is the death>!!"