Who is the killer

Mr.Mutton was killed in his apartment. Mrs.
Mutton called the police. I was cooking soup
and my husband was drinking beer. Suddenly
2 man in masks broke into. They stabbed my
husband to death and tied me up than they
grabbed our money and left. It was 2 hours
ago. I called the police as soon as united the
ropes. Have you touched anything (asked the
policeman)? I only switched off the stove. The
policeman arrested the wife right away. Why?