Interestingly enough, I think the theme that Spica is looking at is Idolism, in which case the Murderer was a fan listening to an idol's music when she committed the crime.
Other similar clues: The Anita Family was Broke. Mamoru clearly had an idol he was enjoying watching shortly after his family died, which the police officer noticed. Spica running into him was during a moment he was likely indulging in idolism. Similarly, Tani-san has an idol he enjoys watching while on break.
My suspicion is that Anita Misa was a former Idol or V-Tuber.
As for the murderer... there's plenty of hints it could be the Boss or Tani-san, but I noticed Spica didn't try to touch them specifically. Meg-san on the other hand pulled herself close, so I'm going to guess that is actually who is guilty.