Justine Damond, 40, was shot dead by Officer Mohamed Noor after she called to report a possible rape in the area on 15 July.
It is still not clear what happened but a search warrant filed by the Minnesota Bureau of Criminal Apprehension provides new detail.
It does not name the woman who slapped the car but says: “After that, it is unknown to BCA agents what exactly happened but the female became deceased in the alley.”
Mr Noor, who was the passenger in the police car, had shot across his partner in the driver’s seat, hitting Ms Damond, a spiritual teacher who was engaged to be married.
His partner has told officials he had been startled by a loud noise just before Ms Damond arrived at the vehicle.
News of the warrant, which was obtained by Minnesota Public Radio, came hours after personnel records were released giving details about Mr Noor’s training.
Mr Noor was hired as a cadet in March 2015, becoming eligible to be a sworn officer six months later.
He obtained a degree in economics and business administration before applying.
While on the force, Mr Noor took a number of training courses and passed all his annual semi-automatic, handgun and shotgun qualifications.
No awards or commendations are listed on his record and there are three complaints against him – one dismissed and two are pending.
He has been on paid leave since the shooting.
State officials are investigating possible criminal charges and he also faces an internal “use of force” investigation.
Following the shooting he was described by police chief Janee Harteau as having completed training “very well” and being “very suited to be on the street”.
Ms Harteau has since resigned over the shooting.