Debbie Quinn, 21, was said to be in “a very bad way” and was simply unable to provide investigating officers with information.
The woman saw her 22-year-old partner Damien Dowdall shot dead at close range at their home in Clondalkin, west Dublin, shortly after 10pm.
Gardaí are trying to piece together any possible motives for the horrific murder and are talking to family members to see if they knew of anyone who bore a grudge against Mr Dowdall.
They have spoken to most of the family, including Mr Dowdall’s parents, Damien and Carol.
It’s understood that neither could think of anyone who would do such a thing, nor any incident that their son had been involved in that might have progressed to the shooting.
The parents told the media on Wednesday that their son was very popular and had a wide group of friends and no enemies.
Garda sources yesterday said Ms Quinn was a “decent girl” and was too traumatised to talk to detectives.
Meanwhile, gardaí sought assistance from the public in relation to a car which may have been used by Mr Dowdall’s two killers.
“Gardaí investigating the murder of Damien Dowdall are appealing to the public to assist them with tracing a car that was seen acting suspiciously in the immediate area of Lealand Road at approximately 10.15pm, which was very close to the time of the shooting,” said a garda spokesman.
The car, spotted by witnesses, is described as a silver saloon car with a 03 D registration.
Detectives are investigating whether there is a link with a number of known drug dealers who Mr Dowdall had been seen with.
Detectives have stressed Mr Dowdall himself was not a criminal.