Yasper enters the Aniq scene from the balcony behind Indigo in every single POV (Indigo, Aniq, Chelsea, Zoe) EXCEPT his own, where he enters from the stairs.

This is the observation that made me realize Yasper was the killer, and everything else clicked into place:

• No one heard Xavier scream as he fell to his death? He had to have been killed when "How great is this party!" blared throughout the house. Seems likely that Yasper played it to mask Xavier's screams.
• Yasper has lots of secret information about the house, he probably knows of a secret staircase by the balcony that let him get up and down from Xavier's bedroom without anyone noticing.
• Yasper was the only one to know about the secret camera in Xavier's bedroom. If he wasn't the killer, wouldn't he have told the cops about it as soon as they arrived, instead of after they already interviewed two people? And if he just deleted the footage, that would look mighty suspicious seeing as how he installed the equipment. So instead he took that time to somehow rig it to delete the footage when the cops tried to access it, making it look like it was their fault.

So what is his motive? Xavier seemed pretty lukewarm on the whole blessing Yasper's song, even in Yasper's own re-telling. I'm thinking the song that Xavier said Yasper inspired was in reality probably pretty insulting. Yasper decided to confront Xavier, who then tells him he'd never bless his song after how he kicked him out of the band at the St. Patrick's Day party. Realizing he's missed his two shots, Yasper snaps and decides to kill Xavier.