I believe the date matters as if the killer thought, ‘It’s now or never.’ IMO, maybe that means he/she (still a possibility it was a she), felt they were definitely going to do it, got their bearings and plan all set and didn’t want to wait until she returned.
Bowie, I believe, was included in the plan as he was ‘always observed’ as the killer made his mental notes while watching her actions. Hurting him was, I believe, just showing the world he was smart enough and tough enough to ‘take care of’ anything that would get in his way, and he was pretty sure Bowie would be with Katie. OR, even as someone who just followed her that night, he made up his mind as he went along that it would prove to ‘everyone’ that he was not a wimp, and could handle anything he had to. I believe this person has no self assurance, and it manifests as narcissistic behavior and the need to ‘prove himself’ to the world. I still don’t feel it was random. Not necessarily a person close to Katie, because that isn’t how any of her friends are, it seems to me, but one of those who knew her in the ‘everyday relationship’ way. Maybe he had a grudge, feelings for her, or hate for gay people or women. Random would fit her being anybody, being a woman, but he couldn’t know her orientation. Random, IMO, may also mean another similar murder should have happened some time in later months. And to me, random means, (without that low esteem), that he might target a person without a dog.