How do you beat guilty party?

By solving all the crimes. Hint: The last mystery is back at the mansion.

1

Play through the last level until you are ready to accuse Olivia Dickens. Olivia will accuse the Chef, so look through the evidence and select "... A long yellow hair, stuck..." to eliminate the Chef and all other suspects with short hair. Olivia will then accuse the Rocker.
2

Go through the evidence for the Rocker and scroll to the second page of options. Select "...in a busy public restroom..." to prove his innocence and the innocence of all remaining male suspects. Olivia will then accuse the Judge.
3

Select "...of those gold gifts, but I..." from the available evidence to prove the Judge's innocence. Olivia will then accuse the Nurse, the last available suspect.
4

Scroll to the second page of evidence and select "...has exactly three traits in common..." This will eliminate the Nurse as a suspect, leaving only Olivia. Watch the final cinema scene to finish the game.

1. Accuse Olivia
2. Prove the Chef's innocence by clicking "taking back that cook book..."
3. Prove the Doctor's innocence as well as the other male suspects by clicking "...in a busy public restroom..."
4. Prove the Maid's innocence by clicking "...a long, yellow hair..."
5. Prove the Judge's innocence by clicking "... It's not the Judge..."
6. Prove the Nurse's innocence by clicking "has exactly three traits in common..."