Neighbor shot my girlfriend's dog

I'll try to make this brief.

Girlfriend hears gunshot in her neighborhood. Notices her australian shepherd is missing. Her and her grandmother drive around neighborhood searching for him.

She finds him sitting under a neighbor's tree. After approaching her dog, she notices that his entire chest cavity has been blown open, but he is still alive and alert.

Her grandmother knocks on the guy's door and asked him if he shot her dog. He denies it and claims that he only own BB guns.

They call the police and the officer shows up and take both sides of the story. The neighbor ends up admitting to shooting her dog. Claims that at the time her dog was in his yard, his female dog, who is in heat, and his son were also in the yard. Claims that her dog growled at his son, so he shot the dog.

I ended up putting him out of his misery, as there was no saving him. He was only suffering.

This was as gentle, playful, and loving dog as they come.

Could she win in court against this guy?

ETA: Mississippi