What is the murder weapon? Why is this disturbing, especially to residents of the River Valley Farm?

The murder weapons were a shotgun and a knife. This was alarming to the residents of River Valley because everyone owned a shotgun.

'Shot four persons in different parts of the house, calmly picking up the expended shotgun shells. Arrived and left the home, presumably with the murder weapon, without being seen.

Bobby said they were looking for the weapons. The knife. The gun.