This is all just my opinion and speculation, but clearly Chelsea and Clay hung around in the same circles. Chelsea worked and was friends with his ex girlfriend and mother of one of his kids. I'm sure her friend/his baby mama has brought up Clay in conversations before - maybe talking about their son or complaining about Clay. Chelsea also strikes me as someone who was shy and strived for many friends, someone who wanted to be liked and included in all of the happenings in those circles, yet someone who is still very innocent, immature, and just not worldly/experienced (mostly because of her young age)...this is just what I interpreted from comments made by her family and friends and the fact that she still lived at home and didn't drive. I think it is possible that Chelsea wanted to be perceived as a "bad girl" - even though she wasn't. And I also see her friends as always wanting to take care of her, possibly because of this innocence.
My point is, and I'm trying to be very careful to word this properly so people don't take this the wrong way, I think it is highly possible that she told people and possibly posted on social media that she liked to engage in certain sex acts that most people would consider strange or outrageous. From this, I believe it is possible that Clay already knew this by word-of-mouth or snooping on social media and this is why he used this ridiculous story as his defense, although it is now obvious based on the testimony yesterday that she was beaten to death and possibly raped.
Also, I was reading comments on Facebook from people who were watching the live stream yesterday. I saw a few comments stating that Clay's current girlfriend/most recent ex-girlfriend is pregnant. This of course could just be gossip and rumor or I interpreted it incorrectly, but I thought I would throw it out there... I really hope I am not starting a rumor.