Is signing for another person's certified mail at the post office illegal?

My landlord recently told me that she had several certified letters which were addressed to me. when i questioned her as to why she would have received my mail, she said perhaps it was due to the fact that she used to live at my address and they may have mistakenly forwarded the letters to her. She then explained that she didn't know they were mine until she signed for them at the post office. She returned them to me and it seems they may have been tampered with. After discussing this with the local post office manager, he explained that the post office never forwardes certified letter notices and provided me with copies of her electronic signature along with her notation where she listed my address -- not her address. Clearly she lied about her address. She is in the midst of a foreclosure -- I've been receiving many letters addressed to her from solicitors relative to the foreclosure which i have been returning to sender. About two weeks ago, the soliciation letters abruptly stopped. I checked with the post office to be sure she did not recently submit a change of address -- she did not. I believe she may have either gone through my mail box and extracted anything that looked like official mail relative to her foreclosure or she personally asked the mail carrier to forward any mail to her coming to my address. the postal manager suggested I file a police report and a report with the postal inspector. A rather lengthy explanation but i need to know if I'm going to be wasting my time since I'm sure she will cover her story at every angle.