Do you think this message was really bad?

My house was robbed by my husbands sister and her daughter a few years ago. My son took it really badly and after he discovered his causing has a fb he sent her this message.

"hi, do you still remember me? You thief, you robbed all of my things with your mom you bitch. I found evidence against you and I can call police and use in court against all of you if I want. Don't spread lies about me with your mom or I can do the same twice as bad, you bunch of tramps.

Bye (:"

Don't you think it was too much? She has a husband and kids now, but still lives with her mom and brother. She used to have bad relationship before the robbery with my son too.
Do you think this message was really bad?
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