One of the friends Bhupendra Patel alleged that Talwalkar was behind Trivedi's murder but "police has so far neither questioned her nor arrested her."
"We have decided to sit on a fast-unto-death to demand arrest of the culprit," Patel said.
Patel was joined by Bhavangiri Gosai and Dipesh Patel. Patel alleged that the murder of Trivedi and attack on Swami Sachidanand in Dantali town of Anand district were planned and carried out on the orders of Swadhaya Parivar head.
Swami Sachidanand also sat on dharna along with them for a brief period, he added.
A big rally led by sadhus would be taken out in Ahmedabad in the next few days against the Swadhaya Parivar, Patel said. Trivedi was killed outside Ellisbridge Gymkhana on June 15. Police has arrested more than 10 people in the case, including state leader of Swadhaya Parivar Bharat Bhatt.
Attack on Swami Sachidanand's ashram took place on July 17 after he spoke against activities of the Swadhaya Parivar. Police has so far arrested five persons in this connection.
Police had recovered a letter written by Pankak Trivedi to US Secret Service based in Dayton, Ohio, in which he had sought protection for himself and his family from followers of "Swadhayay Parivar." Police had found the letter from inside Trivedi's car on May 15 after unidentified persons outside a private club in Ahmedabad clubbed Trivedi to death.
In the letter, Trivedi had alleged that he was being targetted by Jayshree Talwalkar of the Parivar and its followers as he had tried to expose several financial irregularities within the organisation.
Trivedi said he had been part of the Parivar since 1972 and for the last five years had noticed that millions of dollars collected as donations from the United States and United Kingdom for rehabilitation of the victims of Gujarat earthquake of 2001, had not been used for the cause.
He also said that the supporters of Talwalkar were harassing him and his family after he began questioning the irregularities. Several fabricated cases were also lodged against him, Trivedi alleged.
Trivedi had also sought protection from Ahmedabad police in the past, police said. Friends of Trivedi alleged that despite clear indication by Trivedi that he faced threats from the female head of the Parivar, police was not arresting her.
