Investigators found blood in the getaway car used by a gang fleeing a fatal hit and run of a teacher in south Dublin on Tuesday night.
Detectives now believe this DNA evidence will play a key role in the prosecution of the criminals involved.
Special needs assistant Jacqueline McGovern (54) was killed when she was hit by an out-of-control car in Killiney following an armed robbery at a Centra shop just seconds earlier.
"Blood detected in the abandoned car is key," a senior source said last night.
"Gardaí have a clear idea who was behind this crime. Now this vital DNA is crucial to proving it."
It's understood the three raiders involved in the crime are from the Ballybrack, Sallynoggin and Monkstown areas.
The trio, all men in their early 20s, are known to gardaí for involvement in crime, including violent disorder.
Gardaí are probing if the gang who killed the innocent teacher during their getaway went to a local pub in the aftermath of the incident.
Three men were in the speeding car after they carried out the robbery at the Centra shop, Barnhill Stores on Barnhill Road, in Dalkey, minutes before the fatal crash. Ms McGovern and her friend and colleague Audrey Behan (51) were injured when the out-of-control getaway car hit them at 9.20pm on Tuesday at the junction of Ballinclea Road and Avondale Road, in Killiney, Dublin.
The two friends were out having a walk when they were injured by the 'reckless' driver.
The women were rushed to St Vincent's Hospital, where Ms McGovern later died.
Ms Behan's injuries are not believed to be serious and she is expected to make a full recovery.
There were indications last night that the large convenience shop did not have CCTV in operation during the robbery, as it was in the process of being replaced.
Two men armed with a knife held up staff at Barnhill Stores on Tuesday at 9.10pm.
They threatened staff and made off with the contents of the till, believed to be around €2,000.
Following the crash, the three raiders walked away.
But detectives at Dún Laoghaire have now identified the pub - close to the scene of the fatal crash - where the raiders hid out in the aftermath.
Officers have now obtained CCTV from this premises.
"The three men were reported to have been in a local bar drinking pints after this robbery occurred, and they were rattled by all accounts," a source said.
"This is one line of inquiry being looked at by gardaí to establish if these men were involved in the earlier robbery."
The Nissan Almera used by the gang was 'mangled' following the crash.
The getaway vehicle has not been taxed or insured since last April.
Its last registered owner, a man from Bray, was interviewed extensively on Wednesday.
He has told gardaí he sold the car on for a small sum.
His account has been accepted by gardaí and this man is not involved in criminality.
On Wednesday shattered plastic, and scrape and tyre marks showed where the driver of the getaway car lost control, most likely after hitting a speed bump.
"There was one car crashed and another in the middle of the road, and the women were on the ground," one local woman told the Irish Independent.
"I think they were walking on the path but there were three shoes in the middle of the road too," she added.
Ms McGovern was an SNA in the local Our Lady of Good Counsel girls national school.
Ms Behan is also an SNA at the same school.
Both women were prayed for at Mass in the parish yesterday morning.
Principal of the school Caroline Quinn paid tribute to the women.