It was the Family who did it

A popular theory people believe is that in fact it was Susan Nitcher and Frank Rapp who murdered her. Susan and Frank are the former employers of Karina Holmer. Karina had only been working for the few months she had been in America. Prior to her death she sent a letter home to her mom claiming she was cutting the trip short and going home, due to too much cleaning. However she also wrote a letter to her friend saying she was leaving early, something terrible had happened and she would tell her next time she sees her. However Karina never saw her friend again. 

When question the family the nanny working for Frank and Susan made some negative statements towards Frank, making him become a suspect. To further this Frank and Susan lawyer up and became uncooperative with the whole investigation. The next day at 9 PM a fire dumpster, 200 feet from Frank and Susan's condominium occurred. While there was not enough evidence to prove the fire was related many think Karina's clothes and other evidence was destroyed in that fire. 

Further more people suspect the family even more due to some art pieces of Susan Nichter. Some say the paintings made by Susan shows that they did in fact kill Karina. People believe that there are subliminal messages hidden within the paintings that prove that Frank did in fact kill Karina.