Replying to WTF? Ipod stolen ???

So I might be over reacting but this is just crazy. A year ago when I got back from Co I lost my ipod back home. I asked my sisters If they saw it and they said no. After that I moved out of my parents place but recently I moved back in  , like 2-3 weeks ago. Me and my sister never got along well but it was ok. Last week I asked her to take her car because mine was at the garage and she said yes.In her car I found my ipod video 30g that I had lost , all scrashed and fucked. I went inside and asked her why she had it and all stressed she answered it wasnt mine and that she found it in a parking lot . But my name was written in it and when she uploaded music on it she oviously saw it. Anyway I forgot about it and everything went back to normal. But tonight when i got in my room my purse wasnt placed the same way taht it was before so I cheked inside and my ipod was missing with 25$.... I dunno what to do this is going crazy haha omg should I put a lock on my door?