They are sure two shots were fired at Mr Killally and members of his family, though last night they had still to locate the bullets.
Gardaí believe the gunman and at least one accomplice may have been waiting for hours outside the developer’s plush house in Edenderry, Co Offaly, before they struck.
The attack took place at around 10.30am on Thursday as the ex-chairman of Offaly County Council was exiting his driveway in his silver Volkswagen Passat vehicle.
His father, Jay, and two of his four children, daughter Aoibheann, 3, and son Ferdia, 2, were also in the car at the time.
The gunman jumped out of the waiting silver 06-D registered Opel Astra saloon and fired at Mr Killally’s car. Mr Killally drove away from the scene and the gunman jumped back into his car and pursued the VW Passat.
The 44-year-old, estimated from a 2010 bankruptcy to have debts of more than €73m, lost control of his car a short distance later when it overturned after hitting a ditch.
According to an eyewitness, Mr Killally ran into a nearby field and the pursuers tried to get near him but failed. Gardaí were quickly on the scene, but the attackers had fled.
Neither Mr Killally, his father, nor his two children were hit by any of the bullets, but they sustained minor cuts and bruises after the car crashed.
“We are anxious to hear from anybody who may have seen the Opel Astra or anybody acting suspiciously in the area before the incident occurred,” a Garda spokesman said.
An incident room has been set up at Tullamore Garda Station and anybody with information is asked to contact 057 9327600, or the Garda Confidential Line on 1800 666 111.