I think this was planned and the person wore gloves, possibly cut-resistant gloves/arm coverings, and maybe even had gear such as night-vision goggles. I think he watched the house, had been there before (crashed a party), and knew the layout. He maybe killed Ethan first because he was a male and would be a bigger threat if he fought back.
If this was a crime of passion, they would have been sloppy and left DNA all over the place (not been prepared for a knife becoming slippery from blood and cut themselves, or a victim fighting back and scratching them, getting the attacker’s DNA under their fingernails, etc.). I think this person was prepared and left few traces.
I think the person is a young male, strong enough to not get too exhausted knifing multiple people, someone who comes off as creepy or a social reject, he’s envious of more socially successful people and gets angry he is rejected by women, he developed a fixation on one of the girls and the rest are collateral damage. I think he did it alone, this is someone who can’t develop a bond with someone, not well enough to have a trustworthy killing partner.
