A reward of up to £10,000 is being offered to help catch whoever was responsible for a house fire which killed six members of the same family.
Essex Police recently said they suspect there was a burglary at the house shortly before the blaze.
Sabah Usmani, her sons Muneeb, nine, and Rayyan, six, and daughter Hira, 12, died in the fire in the early hours of October 15 at their home in Barn Mead, Harlow.
A third son, Sohaib, 11, and daughter Maheen, three, died later in hospital. Dr Usmani's husband, Abdul Shakoor, was the only survivor.
Crimestoppers said it would pay the reward for information leading to the arrest and conviction of those responsible.
Ann Scott from the charity said: "This is an absolutely heartbreaking incident which has devastated and shocked the entire community.
"It is impossible to imagine how Dr Shakoor, who survived the fire, is coping with the loss of his family.
"Please come forward to the independent charity Crimestoppers so this truly awful crime can be solved."
She added people had "nothing to fear" by contacting Crimestoppers as all witnesses could remain anonymous.
Information is particularly wanted about a group of four males who were outside the house in the early hours of October 15.
They are described as aged between 16 and 19 and wearing tracksuits and baseball caps. There were two others on bikes.
The first is described as 15 to 18 with ginger or light brown hair. He was wearing black jogging bottoms with stripes down the legs, a hip-length anorak style jacket with a hood and was riding a light-coloured bike.
The second was riding a black mountain bike. He is described as 16 to 18 and was wearing a light grey top.
A Ford Focus parked nearby also caught fire around the same time.
A laptop bag containing personal items belonging to Dr Shakoor was found abandoned near lock-up garages in Whitewaits, Harlow, on October 26.
It is thought the laptop might have been stolen in the burglary. Officers are yet to trace his black Toshiba laptop which has a two-pin connection used with an adaptor.
Anyone with information can contact Crimestoppers on 0800 555111.