Police hunting the killer of Christchurch prostitute Mellory Manning say an examination of the dead woman's clothes has found grass seeds embedded in them.
The body of the 27-year-old woman, strangled, stabbed and beaten about the head and legs with a piece of reinforcing steel, was found in the river on the morning of December 19.
It was thought she was picked up in downtown Christchurch by her killer late the previous night.
Detective Inspector Greg Williams said yesterday the forensic team had recovered a range of grass seeds from Ms Manning's clothing, with some seeds being more than 2cm long.
"She had clearly been lying on some weedy type grass prior to entry in the water and it is very likely this was either a direct result of her attack or as she was placed into the water."
Mr Williams said the team had found similar seeds from grass close to the river and they did not appear to match anything at either the Caledonian Hotel carpark or Chester St East carpark where Ms Manning had been earlier on the night she died.
Photographs taken of Ms Manning at Peterborough St in November 2008 showed she was immaculate about her clothing, Mr Williams said.
"If this grass seed has got on Mellory when she was being attacked then there is a good chance that the person responsible could well have also turned up that evening with a significant amount of grass seed stuck on their clothing.
"It is the sort of grass seed that gets stuck in your clothing and is very hard to get out."
Mr Williams said police were yet to hear from anyone who might have made a "large splash" two pedestrians heard before they saw a four-wheel vehicle drive alongside the Avon River about 11pm on December 18.
Both witnesses reported being startled by the splash they heard coming from the area where Ms Manning's body was found.
They said it sounded like someone doing a "bomb into a pool", rather than ducks or geese landing on water.
Moments after the witnesses heard the splash a diesel engine roared to life, Mr Williams said. The pair watched a four-wheel-drive, possibly a dark green or blue Nissan Safari or Mitsubishi Pajero, approach, switch on its lights and drive slowly past.