There is no information about who the killer is here, this is purely all of the evidence you can collect in the game and where to find each piece.

There will obviously be some spoilers for the game here, so be wary of that! I suggest you only will look through this guide after you have done a few playthroughs yourself and/or if you want to find those last pieces of evidence.

If you are interested in finding out how to successfully retrieve the information from your suspects (as in, which options to choose), then you will probably find this guide very useful:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3282898510

• 1: Toby
  
  Toby was on edge all evening
  
  
• 2: Toby
  
  Toby cornered Marcus
  
  
• 3: Bradley
  
  Bradley was in a bad mood that evening

• 1: Lottie
  
  Lottie kept looking out of the window

• 1: Bradley
  
  Bradley's hands were shaking
  
  
• 2: Aunty June
  
  Aunty June was on edge
  
  
• 3: Toby
  
  Toby called Nan in tears

• 1: Aunty June
  
  Aunty June thought Marcus should face consequences
  
  
• 2: Bradley
  
  Bradley tore his room apart

• 1: Aunty June
  
  Aunty June's candle was called "closure"
  
  
• 2: Aunty June
  
  Aunty June hates Uncle Marcus
  
  
• 3: Bradley
  
  Bradley has poisons, the poison must be Polonium or Thallium

• 1: Lottie
  
  Lottie had two phones
  
  
• 2: Aunty June
  
  Aunty June asked Bradley where she could hire a hitman

• 1: Toby
  
  Toby was talking to himself in the toilet
  
  
• 2: Bradley
  
  Bradley was missing little bottles

• 1: Toby
  
  Marcus left Toby no choice
  
  
• 2: Mum
  
  Mum wants to take over the business

• 1: Lottie
  
  Lottie met a man in a hoodie
  
  
• 2: Nan
  
  Nan with a wheelbarrow and Grandad's suit

• 1: Lottie
  
  Lottie handed Uncle Marcus something
  
  
• 2: Mum
  
  Mum offered food to Uncle Marcus

• 1: Aunty June
  
  Aunty June has a temper
  
  
• 2: Aunty June
  
  Aunty June poisoned her flatmates

• 1: Bradley
  
  Bradley still has the Polonium
  
  
• 2: Nan
  
  Nan was in Bradley's bedroom
  
  
• 3: Toby
  
  Toby knew about Bradley's poisons
  
  
• 4: Lottie
  
  Lottie knew about Bradley's poisons