Uses condom to fool authorities; forgets to take his condom with him in order to fool the authorities.
He may also have just raped her,using the condom to try and hide his DNA and then killed her to keep her from talking. Why would anyone give credence to anything this guy says? Maybe she was a moral sleaze, maybe not, but I doubt she deserved to die either way.
Keep in mind there are cameras all over the street/bar/apartment etc... This sounds like sudden passion/anger/rage/stupidity if you ask me. No mention of forced entry and the chick willingly invited the guy up to her apartment. Also, tension between her and her boyfriend. Wonder why, hmmm...