He said he and his friend had just finished eating lunch when Lenihan's radar detected a ute speeding.
"I looked and it was doing 153 and I thought, 'Shit, that's bloody moving'," said Mr Morris. "After the ute had gone, he [Lenihan] said, 'I'll have him'."
Mr Morris said that as Lenihan began to do a u-turn, there was a high-pitched noise and a flash as Mr Brown's 998cc Kawasaki Ninja collided with the rear of the patrol car.
"I saw bits and pieces of bike everywhere and the oil and petrol everywhere ... I started looking for the rider. I went down the road looking for him."
Mr Morris, who suffered a bruised sternum and whiplash injuries, then directed traffic as Lenihan continued the search for the motorcyclist.
Mr Brown, a former motorsport champion, was found lying face down in some grass more than 70m from the crash site.
Senior Constable David Tidmarsh of the Waikato serious crash unit said analysis at the crash site showed a u-turn was impossible and a three-point turn would have taken at least 7 seconds, despite Lenihan believing he had time to make the manoeuvre.
The driver of the ute Lenihan wanted to pursue, Carl Jackson, was Mr Brown's best mate.
The two men had been together earlier in the day visiting a friend.
Mr Tidmarsh said Mr Brown had a blood alcohol level of 56mg per 100ml of blood - under the legal limit of 80mg.
Tests showed he could have been travelling at between 114km/h and 142km/h just before the collision.
Mr Jackson was later cleared of ignoring police signals to stop, because the patrol car did not pull up behind him. He was a pallbearer at Mr Brown's funeral.
The death was a devastating blow for Mr Brown's parents, John and Jenny, who had already lost two other sons, including one in another motorcycle crash.
The defended hearing, which was adjourned yesterday afternoon to allow Judge Lance Moore to visit the accident site, is expected to end today.
