Abdi Laban, 32, died of smoke inhalation at the fire in flats in Balfour Court, Kingsthorpe Hollow on March 31.

The flames ripped through Shoemaker Court at 11pm, reaching the stairwell of the second floor, where Mr Laban lived, and initial investigations suggested the motorbike left in the hallway had caught fire.

However, the inspecter leading the investigation said forensic tests at the scene have failed to establish a cause, leaving police in the dark over whether the fire was started deliberately.

Detective Chief Inspector John Jones said: "We are appealing for anyone who may have been in the Balfour Court area of Northampton on the evening of Monday 31 March to contact us.

"We have discovered the seat of the fire was at the base of the stairs but we still have to determine exactly how the fire started.

"We would like to speak to anyone who may have any information about this fire and would urge anyone who has yet to talk to us about what happened on that night to contact us."

A 14-year-old boy and a 12-year-old girl were arrested shortly after the fire and released on bail but police confirmed no action would be taken against them.

Residents of the flats were evacuated after their individual fire alarms alerted them to the fire.

They have been in temporary accommodation while the building is cleaned and made safe.

Northampton county councillor Liz Tavener has called for statutory smoke alarms in communal areas of blocks of flats to avoid another tragedy.

She said: "No tragic death like this must ever happen without lessons being learned."