Context: I'm walking with my friend, my friend sees something mean written on the wall for example, he says "Why would someone do this?.", how should I understand it? as:
1-" Why someone did this?."
2-" What motivated someone to do this?."
3-" Why would it occur to someone to do something like this?."
4-" What reasons someone had to do this?."
If none of the 4 sentences above is correct, please tell me what it means.