Re: Why would..

To truly know why the one neighbor would kill another, you must know the victim. Who was he/she? Did s/he have annoying habits? Was s/he mean, spiteful, rude? Did s/he have some secret knowledge about the killer that the killer sought to protect from exposure? Was there some action (such as your idea of stealing a past lover) which the victim performed that built a revenge need in the killer? Was the neighbor rich and/or powerful and connected to the killer in such a way that the killer would gain said money or power if the victim died? Did the victim have a gorgeous spouse with whom the killer had fallen in love, and the killer sought to eliminate the competition, or conversely, rescue the spouse from the victim's alleged abuse? Was the killer just crazy and didn't like the way the neighbor grew his/her roses or let his/her tree branches drop leaves in the killer's pool? A killer ALWAYS feels he or she has something to gain by killing, even if no one else understands it. In his or her mind, the end justifies the means.