<human>: this is my first post here, I'm looking for some advice on a letter that I got in the mail today.
I received a letter today which seemed to be the ordinary except that it had the post code written on the front of the envelope in pen which I thought was strange.
when I turned the letter over it has clearly been opened already and the person has sealed it again with two bits of sticky tape. 
i quickly noticed the sticky tape has blood underneath it. kind of like in lines or something,
like some one has scrapped their finger along the end of where you rip the tap off on that spiky bit.
 I don't really understand this and havent opened it because it just seems really strange.
 what makes it stranger is that a package for a ex-housemate who had it in for me and my friend really bad, for no reason, i think she had some mental issues and i know that she was a heavy drinker and valium user, she has threatened both me and my friend on countless occasions, not to mention going crazy one day and calling the police on us, when it was her yelling and screaming. well the package for her arrived in the same mail today. and she hasn't lived here for months now. it's the first mail to her since she left.
so yeah that is what has happened.
do I go to the cops. do I just get rid of the letter? idk

Could you distill the essence of the text into 1-3 sentences?
<bot>: got a letter sealed with sticky tape that has blood under it. crazy lady I used to live with might be involved. havent opened said letter. what do