Diphu/Nagaon, May 23: The investigation into the suicide of five sisters in Diphu town of Assam two days ago remained in the realm of speculation with police saying the girls may have been acutely depressed and psychiatrists failing to go beyond describing the act as a rare psychotic phenomenon.

As people tried to make sense of this tragedy of epic proportions, the shocked family — the siblings’ parents and their brother — cut themselves off from the rest of the world.

Anuradha (31), Jaya (29), Nilakshi (26), Nabanita (23) and Priyambada (18), daughters of retired public health department executive engineer Umesh Chandra Bordoloi, hung themselves from ceiling fans at their Diphu residence on Friday. The eldest of the daughters was married less than two weeks ago and had come to her parents’ home because she was to sit for an exam.

A neighbour, Ramen Gogoi, said all five were “level-headed girls”, though they used to keep to themselves. “Nobody could have imagined they would commit suicide. We were stunned on hearing about the tragedy.”

A girl who identified herself only as Rashmi said she knew one of the siblings well. “My friend and her sisters never appeared suicidal. All of them were so soft-spoken and nice to everybody.”

A relative of the family, Mohan Bordoloi, said Anuradha “received a shock” immediately after her marriage. “She discovered that her husband was not a teacher, as he had claimed before marriage. We do not know exactly what he does for a living, but we suspect he had lied to us.”

Bordoloi said Anuradha’s “bitter experience of a short conjugal life”, coupled with the overwhelming emotional support of her four sisters, might have psychologically driven them to end their lives together. “Till 11 pm that night, all five were enjoying a television programme with their brother. Before committing suicide, they destroyed all their photographs.”

Diphu police interpreted the suicides as a manifestation of collective depression, perhaps brought about by Anuradha’s plight after marriage. “We think they were introverts and had an intense emotional understanding among them,” superintendent of police Pankaj Sarma said.

The officer said the investigation would surely bring to light the exact cause of this depression.

Deputy superintendent of police Hitesh Roy, who is leading the investigation team, said this evening that he was yet to receive the post-mortem reports. “Going by available evidence, the girls definitely committed suicide. But there is an element of mystery about the motive.”

A senior doctor said five mature, educated girls of a family committing suicide together was a phenomenon that could not be demystified easily.

Anuradha’s husband Phani Bora reached Diphu yesterday and lit the funeral pyre. Her four sisters were cremated together.