Rosemarie Fritzl has refused to file for divorce from her pervert husband, according to her sister.Christine Ranner told Austrian daily Österreich yesterday (Sun) Josef Fritzl asked her in a recent letter correspondence to find out whether his wife would agree to get divorced.Ranner, 57, said Fritzl who kept his own daughter as a personal sex slave in a basement dungeon for 24 years told her he wrote eight letters to his wife checking whether she would agree to split. The couple is, in contrast to contrary reports, still married.Ranner, who lives in the Upper Austrian city of Linz, said: “My sister decided not to file for divorce since this would be Josefs final triumph over her. It would mean she would not receive any pension if he passes away before her after 55 years of marriage.”Asked why she wrote to her 75-year-old brother-in-law, who according to a former cell mate considered killing his cellar dungeon family in an acid bath, Ranner explained: “He was the only one who helped me when I was in financial trouble 29 years ago. I was a single mum and urgently needed 1,500 Schilling (110 Euros). He gave me the money and even cancelled my debts at Christmas. Ill never forget that.”Ranner also revealed Fritzl has failed to say he is sorry for his crimes. The incest dad wrote to her: “Only those directly affected can write about feeling sorry and about their feelings. What happened was never planned. I need to carry the guilt all alone. I have to say that I would rather stick to strangers who have more trust in me than my whole family together.”Fritzl was arrested in 2008 and sentenced to life in prison last year. He is serving his spell in Stein prison in the Lower Austrian town of Krems.The former family home in Amstetten is likely to be destroyed after liquidator Walter Anzböck could not find an investor, according to bankruptcy trustee Markus Sonnleitner.