Donald Bennett, 83, had just bought an ice cream in Pudsey Park when he was killed.
He suffered 38 injuries and was pronounced dead after a police van rolled down a slope and hit him in June 2013.
A boy who was 12 at the time said he looked through the passenger window of the vehicle and saw the female officer motion as if she was pulling up the handbrake.
The boy - who cannot be named for legal reasons - said: “I turned around after my friend screamed and saw an elderly man was halfway down to the floor as he was being hit by the van.
“I ran over to the van with my friend and looked underneath and saw blood coming out of the elderly man’s head.
“I also saw the police officer run past us and go around to the driver’s side door.
“I saw her lean into the van and it looked like she was doing the motion of pulling the handbrake up and then she came out and went to the front.”
The young boy added: “I was at the passenger side and looking through the window to the driver’s side.
“I wasn’t tall enough to see what she was doing fully.”
The inquest in Wakefield heard Pc Claire Bugler had been called to the scene in a park in Leeds after a disturbance involving the boy and others.
The youngsters had been messing about in the toilets of a wildlife centre and claimed that a keeper had grabbed one of them by the throat.
The youngster described how Pc Bugler arrived and went inside the centre with the keeper to discuss the incident before a friend screamed that her police van had rolled down the hill and hit someone.
He said PC Bugler then came back outside and ran to the scene and appeared to apply the brake.
Questioned by PC Bugler’s representative, Alisdair Williamson, the lad admitted he had not actually seen the handbrake and had just seen PC Bugler move her elbow towards her as if to pull something up.
The inquest was also shown CCTV footage from the ice cream van that was close to where the police van came to a stop.
A number of Mr Bennett’s relatives had to leave the court as the footage was shown and those who remained became emotional when Mr Bennett appeared in full view of the screen to buy his ice cream.
Mr Bennett walked to the ice cream van at 2:01pm holding two walking sticks and ordered a flake.
Shortly after, at 2:05pm, a police officer could be seen walking past the shot.
At 2:06pm the police van rolled into view from the left hand side of the shot.
It appears to show something being dragged underneath, although Mr Bennett could not be seen clearly in any of the shots.
Further footage showed a group of men rush into view.
Around five or six men put their hands on the bonnet of the van, and appeared to push against it. The van moved backwards.
After a few seconds, more men arrived and they tried to lift the van up, appearing to try and free Mr Bennett.
Mr Williams has requested details of the CCTV to be viewed again during PC Bugler’s afternoon evidence to determine if PC Bugler can be heard saying: “The handbrake’s on.”
The inquest continues.