Why was Guy Clarendon killed?

There are two ways to answer the judge's question.  You can work out the
answer or you can use process of elimination.  Although there's a perfectly
logical way to solve this, it depends on your knowing the answer to another
of the judge's questions.  Since I don't want to answer a future question
for you, I'll use process of elimination.  Holmes will explain after the case
is over if you want the explanation.

Clarendon didn't have any money, so Loretta wouldn't kill for it ("E").

Several people told you about the nature of Loretta and Guy's relationship.
Both Langdale and Loretta gave you some important information.