The murder weapon is a red lanyard. We know the killer owned the lanyard, because Evelyn was found wearing her own red lanyard (a different one).

Read the Resident Memo.

Read the Resident Database.

Diane can be ruled out. All residents who moved in after March 1st, 2022, received orange lanyards, not red ones. Diane moved in to Saguaro Sands on March 2nd, 2022, so she received an orange lanyard. Diane did not have access to the murder weapon (a red lanyard), so she isn't the killer.

*Also, there was two sources of DNA on the red lanyard — Evelyn's, and the killer's. We can assume the killer owned the red lanyard (as opposed to borrowing it from another resident) because they were the only other source of DNA on it (besides Evelyn).