In the letter Jiah Khan talks of aborting her baby and blames Sooraj Pancholi for the troubled relationship.
According to the Indian Express, her family members were not happy with police investigations.
Jiah Khan's younger sister Kavita, who came to Mumbai from London told the newspaper that "The six-page letter has been handed over to police. We wanted Jiah's voice to be heard by the world."
Family members said there were several indications in Jiah Khan's letter about her troubled relationship with actor Aditya Pancholi's son Sooraj but police investigation was tardy and shoddy.
"My mother and sister have recorded their statements with police and told them about the relationship between Jiah and Sooraj," said Kavita.
"Jiah Khan was not depressed regarding work. She was the strongest girl I knew. She was my strength," said Kavita, Rubbishing media reports about Jiah Khan not getting films. She said the last time they spoke, Jiah seemed happy as she had got a few offers.
Cherring Dorje, Deputy Commissioner of Police (zone 9) told the newspaper that the "investigation will not be biased. The contents of the letter cannot be disclosed at the moment. We are taking legal opinion on the matter."
Juhu police have said they have recorded statements of eight people, including Sooraj. They have also retrieved SMSes, records of phone calls exchanged between Jiah and Sooraj minutes before she hanged herself, her social network conversations and the letter.
"We are now waiting for forensic report to confirm Jiah Khan's handwriting to see whether the case can be changed from accidental death to abetting suicide," the newspaper quoted an officer.
Excerpts from the letter allegedly written by Jiah Khan:
I aborted our baby when it hurt me deeply.
All you want in life is partying, your women, your selfish motives. All I wanted was you and my happiness. You took both away from me. I spent selflessly on you.
I have nothing left to live for in this world after this. I wish you had loved me like I love you. I leave this place with nothing but broken dreams and empty promises. All I want now is to go to sleep and never wake up again.