Key evidence was unwittingly destroyed at the start of an investigation into the deaths of six family members in a house fire in 2012, according to an investigator who worked on the case.
Dr Sabah Usmani, 44, and her five children – Hira, 12; Sohaib, 11; Muneeb, nine; Rayyan, six; and Maheen, three – died following the fire at their home in Harlow, Essex. Her husband, Dr Abdul Shakoor, survived the blaze.
A fire investigation officer has told a BBC podcast that a forensics contractor allowed crucial evidence to be put in a skip, while another investigator claimed samples were packaged incorrectly.
Essex Police said it could not comment on the claims as the investigation was still live.
David Hadjicostas, then a fire investigation officer for Essex Fire and Rescue Service, said the forensic science adviser from Key Forensic Services failed to test the external lock on the family's front door, which Dr Shakoor and his neighbour reported was open.
Dr Shakoor told officers there was a problem with the door's lock, which prompted the police to consider an opportunist burglar.
Mr Hadjicostas said he saw the adviser try the lock on the inside of the door, but not the outside.
"I always thought that was particularly odd because he was adamant that the door was lockable and he only tried 50% of the lock," he said.
The door was removed from its frame and put in a skip before the fire team had examined it, he added.
In the early hours of 15 October 2012, the family, originally from Pakistan and who moved to the house in Barn Mead in 2011, awoke to a loud sound and thick smoke.
After trying to raise the alarm from a bedroom window, Dr Shakoor jumped out to seek help. Firefighters later had to restrain him from going back into the property.
A neighbour's car had been set on fire at the same time.
Police at first suspected arson, but 11 days after the fire, a laptop bag containing photos belonging to the Shakoor family was found dumped at a nearby estate.
Officers then launched a murder investigation, believing someone had burgled the family home and stolen the laptop before setting the house on fire.
After receiving complaints about work undertaken by Key Forensic Services, Essex Police appointed Iain Peck, a specialist fire investigator from Prometheus Forensic Services, to review it.
Mr Peck said he was disappointed by the way samples of a large piece of laminate flooring in the lounge, where it was believed the fire started, had been taken.
"Whoever was doing the packaging had stuck a nylon bag over one end, another nylon bag over another end, and then used Sellotape to kind of make some sort of Christmas cracker."
The samples were rejected as they needed to be airtight so they could retain vapour from any potential accelerant used, he added.
Mr Peck said the neighbour's car, a silver Ford Focus, which had been set alight the night of the fire, had not been fully excavated and appropriate samples had not been taken within 24 hours.
Prometheus Forensic Services complained to the Forensic Science Regulator at the Home Office at the time about Key Forensic Services' work.
However, the regulator said although a code of practice and conduct was published in 2011, it did not cover fire scene investigation.
