Spoiler

It just seemed to me people were confused about this movie so thought I'd throw in my two cents.

Ellie spied on her mother and Lawson, she loved her dad and didn't want him hurt so when her mother began packing to take herself and the girls away Ellie snuck into the house...The mother was not answering Lawson's calls so he became angry and hit a golf ball into the house. Ellie took her mother's distraction to murder her.

Ellie wanted her father to be loved so she felt she had to step into the role of lady of the house. I think she was afraid of another woman hurting him is why she didn't want him with the other woman.

At the end, she was ignoring Lawson as her mother had...so again he hits a golf ball into the house. Later he comes to the door, remember the doorbell...

As Ellie is going to the door Inger murders her. Inger was always jealous of her sister and father and was angry that Ellie murdered their mother. Inger than quickly disappears...

Lawson comes in and finds Ellie, he picks her up and wants to help her.....

But you have a trigger-happy cop who comes in and shoots without assessing the situation first. In real life no cop would shoot without first at least saying "stop" "put her down" "hands up"...anything. So that scene was just wrong!

The father is a big coward who can't stand up to his girls...so we can gather that Inger will walk all over him as well and that his new wife will also end up dead.

My personal opinion...the real person responsible for the murders...The Father!!!