Three men threatened staff with knives and swords and smashed open display cases at the Hamilton & Inches store in George Street, Edinburgh, on the morning of Friday June 6.
More than £800,000 of jewellery was stolen from the window displays of the shop alone, with a £325,000 diamond Chatila necklace the most expensive item taken during the incident.
A full inventory of what was stolen is continuing to be drawn up, but Chatila earrings worth £95,000, eight Patek Philippe watches ranging from £22,000 to £66,000 and diamond rings worth £61,000 were also taken by the gang.
The robbers, who were all dressed in dark clothing, made their escape in a white BMW car driven by a fourth man and that was later found abandoned in Gloucester Lane.
Police have now recovered a second car which was used by the gang after they left the BMW.
Officers believe at least four people would have been travelling in the dark blue Honda CRV, which is thought to have been driven north along Gloucester Street on to Kerr Street, then through Stockbridge towards Raeburn Place.
It was recovered abandoned in a car park at East Pilton Farm Rigg in Edinburgh.
Police are appealing for anyone who saw the car, thought to be a 2007 model, on June 6 to contact them.
Detective Inspector Carol Craig said: "The response we have had from members of the public to this very serious incident has been terrific so far.
"But those responsible have still to be identified and we hope that the recovery of the dark blue Honda CRV could prove crucial. We are appealing for anyone who may have seen the vehicle being driven in Stockbridge around the time of the robbery or being dumped at East Pilton Farm Rigg to come forward.
"This was clearly a very high-value robbery and the items involved very precious pieces of jewellery. It was also a frightening experience for the staff at the shop and we are working hard to establish exactly what happened."
Robert Kirk Inches and his uncle James Hamilton opened their first premises at 90A Princes Street in Edinburgh, under the name Hamilton & Inches, on November 10 1866.