A 22-year-old woman from Furbo was killed in an incident on the Barna/Moycullen Road junction overnight.
A second woman, also in her early twenties, was also found at the roadside and is in a stable condition.
Gardai now believe they fell from a moving van after the rear doors opened. It is understood there were seven passengers – two in the front and five in the rear. The van has been recovered and is being examined by Garda Forensic Collision Investigators.
The two women were discovered at around 2.20am today.
The deceased has been named locally as Cliodhna Thornton.
They both received medical assistance at the scene and were taken to University Hospital Galway. One of the women was later pronounced dead. A post mortem is to be arranged. The second woman remains in a stable condition.
The scene was preserved for technical examination and to facilitate Garda Forensic Collision Investigators.
No arrests have been made. Investigations are on-going.
An initial theory Gardaí were working on was that there had been a hit-and-run, but this was later discounted as the investigation progressed. There was no vehicle at the scene, but a van was later recovered.
Gardai are appealing for witnesses or anyone with information, particularly those who may have been travelling on the N59, Galway-Moycullen Road or the Barna-Moycullen Road, between the hours of 1.45am and 3.15am, to contact them at Salthill Garda Station on 091 514720, the Garda Confidential Line, 1800 666111 or any Garda station.