Dagorlad has some good ideas.
Here's some from me as well:
Maybe one of the rats could have a pair of runes branded onto it's back. The PC's stencil them down and show them to Eldarron. He appears shocked and horrified by it; he draws in his breath to speak, but as he is about to speak, a poisoned dart shoots from the cave mouth and hits him; he dies within seconds. If the PC's look fast enough, they will see a small, shadowy figure for a handful of seconds before he bolts off. If they attempt to follow him, he will easily escape, obliterating his tracks as he goes, and shoot at them with his crossbow. The PC's must attempt to find him and find out why he killed Eldarron and, hopefully, what the runes on the leather mean.
Another idea:
Eldarron lives and tells the PC's that he is grateful for their assistance. Just then, two men show up; both are heavily armored and carry big weapons. They demand payment from Eldarron; he refuses. They will attempt to attack Eldarron with their maces and, if the PC's try to stop them, they will fight them too. If they survive, Eldarron tells them that he has learned a spell to grow diamonds; the men have been extorting them from him for some time. On the latest occasion, he refused to and they beat him, which could be the reason why he was dying. Eldarron says that there are more men, and they have also had control of the local town for some time.
Just some ideas.