I also would find it surprising if this was his first murder. If it was, then boy his first step was a real doozy. If I were LE I would definitely explore other victims with him directly and by investigation.
Many cases on here evoke emotions of sadness for the victims and their families and anger and hatred for the perps. This one has suddenly brought on feelings of outright disgust, abhorrence and disbelief. I, like many, have begun to question our world and humanity itself. It is completely understandable to feel like the world is falling apart. However, the fact is that people like this have always existed, even in the "good old days." The 20th century alone has scores of examples where individual political figures and groups have killed tens of millions of people in the most grotesque fashion. Hitler, Stalin, Mao, Pol Pot, Ho Ch Minh, etc. There are scores of serial killers as well that we are all familiar with. If you google top serial killers of all times you will see that throughout the centuries there have some absolutely horrific examples of people doing things even worse to their fellow man/woman than even this and on a massive scale. So, as much as we don't understand when things like this happen, the reality is that for some reason, this has been tragically a part of the human experience. the good news is that there are many good people as well. People who have been blessed, yes blessed, with a tremendous amount of empathy for other. I suspect that many who are on this board fit that category. I have always liked the quote, "The only thing necessary for evil to prevail is for good people to do nothing." Thank you all for not doing nothing.