Murder can sometimes happen for trivial items. In most cases, it happens when a person is already highly strung, and the latest sort of conflict pushes a person over. When there are guns involved, it can turn deadly. This happens even within families, especially when there is some kind of tension involved. It gets really problematic when there is an ongoing tension and this keeps on impacting the people involved in this kind of tension, putting them at a point where they can snap at any point of time.
In this case, the dispute was so bad that the person actually killed his own family members, apparently over something as trivial as a dispute over a washing machine; when there is easy access to guns, the person over the top can suddenly take access to these guns and do something dramatic and tragic during the impulse (link to article):
A man shot and killed his wife and two others in his home on New Year's Eve before his son wrestled the gun away and fatally shot him in a chain of events apparently set off by a dispute over a washing machine, authorities said Friday. "It looks like it was a dispute between the dad and the son's girlfriend, probably over using the washing machine," Sheriff's Lt. John Corina told the San Gabriel Valley Tribune. "For some reason, this set the dad off." The son, 33-year-old Christopher Morey, eventually recovered the gun from his father and shot him, authorities said. Morey is being held on suspicion of murder on $1 million bail, authorities said.