The inquest had heard that all eight brakes on the 10-ton tipper truck owned by Fewston Transport Ltd of Skipton, North Yorkshire, were defective when it crashed into a car and a BT van before ploughing into shops and houses in Sowerby Bridge, West Yorkshire, last September.
At the hearing in Bradford, the coroner, Mark Hinchliffe, exonerated the driver of the lorry, Derek Waterworth, 63, who died in the crash. The other victims were Peter Stott, 42, a BT engineer; Ann Crossley, 32, and her two-year-old daughter Karen; Beryl Rose, 46; and Angela Rook, 28.
Mr Hinchliffe said he had found a 'high standard of proof' that the lorry's owners were grossly negligent. The inquest was told that if the brakes on the lorry had been properly inspected the defects would have been observed.
Mr Hinchliffe said one or more people at Fewston Transport had a duty to have regard to the health, welfare and safety of road users and the public at large which had been breached by the failure to ensure that the braking system was in good working order. This, he said, was the cause of the six deaths.
'That breach of duty arose from gross negligence to such a degree which should, in the opinion of this coroner's court, justify a conviction,' said Mr Hinchliffe.
He went on: 'I find the brakes were so grossly deficient that taking into account the circumstances, the failure to ensure their maintenance created an obvious and serious risk that death would directly result . . . In my view this all adds up to involuntary unlawful killing.'
The coroner said the lorry had gone 49 working days since its last full safety check, and it was not the only lorry 'slipping through that particular net'. He said he would write to the Transport minister asking him to look at all aspects relating to the case and the inspection of brakes on lorries.
Earlier, he praised the lorry's driver. 'I find no evidence to suggest Mr Waterworth's driving exacerbated this in any way or that he knew the brakes were deficient when catastrophe struck. He did all in his power to avoid this tragedy,' he said.
Inspector Gary Walsh, who headed the police investigation, said later: 'As a result of the verdict it is now my intention to have further discussions with the Crown Prosecution Service, to assess the most suitable way forward in respect of this matter, and Fewston Transport and its directors.'