Police are taking lessons on "Kriya Yoga" and reading a book on the life and teachings of Paramhansa Yogananda to figure out how the Des' minds worked.

Debjani De and her brother Partho were associated with the Yogoda Satsanga Society of India that Yogananda had founded in1917.

A team of police officers visited the Satsanga Society's Dakshineswar ashram and talked to leaders of the order for an hour and 20 minutes.

The officers left carrying books on Kriya Yoga and two copies of Yogananda's Autobiography of a Yogi. Debjani apparently practised Kriya Yoga, which has been described in the book as "a form of meditation that consists of a number of levels of Pranayama accomplished by disjoining the course of inspiration and expiration intended to rapidly accelerate spiritual development".

Debjani had become a member of the ashram in 1997 and brought Partho along with her three years later.

Two photographs of Yogananda, who had taught meditation in the US and other countries between 1920 and 1952, were found beside the skeleton, believed to be of Debjani's, in Partho's room in the family's Robinson Street house last Thursday. Many photographs of the guru were later found in the house and also on the dashboard of the family's car.

An officer of Shakespeare Sarani police station said the sleuths were trying to understand the teachings the brother-sister duo had received from the society and whether they had any adverse effect on their minds.

"The teachings are a bit complicated. So our officers have brought some materials that they will read and try to understand the teachings," the officer said.

Among senior leaders of the society the sleuths talked to was Swami Suddhananda, who has been in charge of the ashram for three decades.

The police said they had specifically asked the leaders whether they used to ask devotees to fast or their teachings included anything about life after death. "The leaders said their teachings mention about occasional fasting for a day or two, but make it clear that it should be practised in consultation with a doctor," said an officer.

Though the order denied preaching sustained fasting, chapter 46 of the Autobiography of a Yogi speaks of a woman yogi, Giri Bala, who practised a form of breathing exercise that allowed her to live for over 60 years by only drinking water and without eating anything.

Similarly, the ashram said its teachings never focussed on life after death, but chapter 43 of the book speaks of resurrection of Yogananda's guru Sri Yukteswar, days after he had died and was buried in Puri. According to the book, Yukteshwar appeared before Yogananda while he was sitting in a hotel in Mumbai and gave him lessons about life.