There were three cities of refuge in Eiver haYarden alone and another three for all of Eretz Yisrael. It seems that that Eiver haYarden had a disproportionate share of murderers compared with the rest of Eretz Yisrael. I heard an interesting thought from R' Meir Goldvicht as to why this should have been the case. Bnei Reuvain and Gad made a deal with Moshe. They told Moshe that they will leave behind their cattle, their wives and children, and lead the rest of Bnei Yisrael in battle on the condition that they can have the land of Eiver haYarden. When he accepted the deal, Moshe corrected one thing they said. He told them to build cities for their wives and children and a place for their cattle -- a home for their children is the first priority, cattle second. Although Bnei Reuvan and Gad got the message that their children's needs were paramount, the fact is that for the long campaign of the conquest of Eretz Yisrael their children grew up with no fathers. Most of the male population served as soliders and there was no one home to help raise families. As a result, the society of Eiver haYarden was tainted in a way that other communities were not.
Nedarim 22 records that Ula witnessed the murder of one of his travelling companions en route to Eretz Yisrael. The gemara asks how this could be -- the pasuk of "v'nasan Hashem lecha shem lev ragaz" applies to Bavel, not Eretz Yisrael. The gemara answers that the murder happened before they had crossed the Yarden. It seems from this gemara that there is a segulah aspect to Eretz Yisrael not being a land in which murder occurs.