One of the important characters could be a local guide or informant. This person has knowledge about the diamond mines and the illegal operations. They help the journalist or the person trying to expose the blood diamond trade. There might also be an international diamond trader who is initially oblivious to the origin of the diamonds but later becomes aware and has to make a moral decision. And, of course, the miners themselves are crucial characters. They are the ones at the bottom of this cruel system, forced to work in dangerous and inhumane conditions just to extract the precious stones that fuel the conflict.
There's probably a diamond miner who endures hardships in the mines. And a rebel leader who uses the diamond trade to gain power. Also, a journalist might be an important character as they usually play a key role in uncovering the truth about blood diamonds.