Karachi police on Wednesday identified a toxic gas as the cause of death of five siblings and their aunt whose demise last month had initially been linked to the food they had consumed from a local restaurant.

According to DIG Karachi South Sharjeel Kareem Kharal, the six had died after exposure to toxic gases released in fumigation carried out by the staff of Qasr-i-Naz, an official guesthouse where the victims were staying on their arrival in Karachi from Balochistan.

DIG Kharal, addressing a press conference, said that nine persons, including the chief engineer of the guesthouse, have been arrested on the charge of manslaughter.

The South police chief, while quoting laboratory reports of samples collected, said that phosphine was found in the viscera of the deceased. He ruled out the possibility of toxic food behind the tragedy.

“Phosphine was detected in the blood and stomachs [of the deceased]," said DIG Kharal, as he read out Punjab Forensic Science Agency (PFSA) and HEJ Karachi University's reports. "Drugs/poisons were not detected in blood and stomach."

"Phosphine is an extremely poisonous gas. It is widely used as an agriculture fumigant,” he explained.

The DIG South pointed out that during the search of Qasr-i-Naz's stores, police investigators had found empty bottles of phosphine and seized the same as evidence.

The senior officer revealed that the staff of the guesthouse had allegedly tried to destroy the evidence.

The nine held suspects, including chief engineer Nadeem Shaikh, have been booked under Section 322 (punishment for qatl-bis-sabab: whoever commits qatl bis-sabab shall be liable to diyat).

Kharal said that since the held suspects had tried to disturb the evidence, the police had also invoked Section 201 (causing disappearance of evidence of offence, or giving false information to screen offender) of the PPC against them.

Referring to laws regarding the use of hazardous substance, Kharal observed that the staff was not supposed to use such substance for fumigation purpose as its use is limited to agricultural purposes.

He further said that the investigators were also looking to see as to who purchased as well as provided such hazardous substance.

The five children — three brothers and two sisters — and their aunt had died on February 22 last month.

As police had initially linked their deaths with the food they had consumed, the Sindh Food Authority had sealed a branch of a popular restaurant, from where the victims’ father, Faisal had bought biryani for the family.