Peter immediately knew that the police officer had shot her. But how did he come to know?

Question

A man entered his house and was about to hang up his coat when he heard his wife shout;

“No John! Don’t do it!”

There was a shot and he could hear his wife fall down.

When he entered the kitchen he saw his wife and the gun lying on the floor.

There was a police officer, a doctor, and a lawyer standing next to her.
Peter immediately knew that the police officer had shot her.

But how did he come to know?

Answer 1

The police officer was the only man while the doctor and lawyer were ladies.
Peter on a second glance would also read the police officer’s name on his name tag as “John”.
Peter’s wife was saying, “No John! Don’t do it!” to the police officer and the police officer shot her anyway.

Answer 2

I guess the police officer was responsible for the shooting. He most likely was the only person carrying a gun.

Answer 3

Only a POLICE OFFICER will be having his NAME BADGE in his shirt.