As long as the murderer doesn't mention it to anyone, who would know the whereabouts of the victim? If the body ends up at the bottom of the cliff, it's very likely to be devoured by wild animals within half a day. How could it be such a coincidence that someone just happened to discover the body at the bottom of a cliff within that time frame? Not to mention ... even if someone did indeed find the body, that person might not necessarily report it to the officials. Why would anyone want to be involved in a homicide case that has nothing to do with them? What if the officials, eager to close the case, simply arrest the person who reported the body as the murderer and torture them into confessing to a death sentence? Such occurrences were not uncommon back in the day.
In short, in that vile old society, unresolved murder cases were as common as hairs on a cow. Boss Di's sentence "there might not be a truth to be found" ... was nothing but the harsh reality.
