I apologize if my theory has already been thrown in the mix. Just now got to be able to get on Web.
Some of the things I have thought of could it be a member of the church? I do know my family are all committed to the church of Christ, I'm the oddball Baptist.. I am not sure about this particular church but the ones here the congregation are very devoted to the rules and teachings of the church. Here coc members are kind but very stand off with non members the church is very plain inside they do not use their building for anything other than worship. They do not have a fellowship hall all is done outside the church. They take care or their own and do not provide outside the church to charity. Also I know if a member has been caught say cheating on their spouse if they wish to reconcile and stay in the church they must stand before the church and confess and ask that the members accept their apology it has gotten real uncomfortable once a couple members had to ask for the church's forgiveness when they were caught together and they and their families were all members.
With that said here is my theory
Was a member angry that this woman was allowed to use the building and of course being mentally disturbed no sane person does this stuff but felt it was so wrong and degrading a fitness class was allowed to be held there decided decided to handle it?
Also could it had been a spouse that her husband may have been involved with the lady killed? Even if MR was not a member it would still be a disgrace? If she was not a member it would also be a issue with someone that allowed to use the church for profit and it tainted their sanctuary all though they call it a building but you know what I mean.
These are my theories and not directed towards the denomination in anyway or insulting them, I love my family my own husband are coc they are some of the most devoted Christians out there, but no matter what there are mentally insane people that may seem normal on Sundays but a lunatic outside the doors of the church.
This church may have been more liberal than the ones here.
Just a thought please no one think I'm picking on their beliefs because that would be the last thing I would ever do I respect all that believe in Christ and try to obey the word.