Constable Mark Rodgers, of the serious crash unit, said police want to piece together what happened for the injured woman's family.
"It's difficult to put the jigsaw puzzle together without independent witnesses," he said. "We need to put it together for her family so we can tell them without a shadow of a doubt what happened to her."
The CCTV film shows the cyclist approaching the intersection in the left-hand lane on Quay St, then moving across to the middle of the lane as she approaches The Strand.
The 4WD and trailer then approach the same intersection in the middle lane and a Holden Commodore comes up behind.
Mr Rodgers said police had spoken to all the drivers who were directly involved in the crash.
But they also needed to speak to independent witnesses.
"More interestingly for us is that it shows another vehicle approach behind the cyclist before the lights turn green, which appears to be a dark-coloured convertible vehicle with the roof down," he said.
"That particular driver would be of enormous help to us if he or she were to come forward."
About 11 other cars which came up behind the other vehicles involved in the crash would have had a clear view.
Police also want to talk to the people who went to help the injured woman after the crash.
Police do not believe anyone else was directly involved with the crash and are not looking for people to blame, Mr Rodgers said.
"It's just purely what they've seen, what they've heard, or what they did.
"We're not pointing the finger at them, we're not accusing them in any way of being responsible for the crash," he said.
"Even the smallest part of information ... it all helps with the jigsaw."
How to help
If you saw the crash, contact Constable Mark Rodgers on (09) 359 3116 or mark.rodgers@police.govt.nz
