The court trying Ian Huntley for the murders of Holly Wells and Jessica Chapman has been told the two girls were probably asphyxiated.
Holly Wells and Jessica Chapman's bodies were found in a ditch
Richard Latham QC, prosecuting, said it was impossible to determine the precise cause of death, or whether the girls were sexually assaulted, because of decomposition.
But he said there were no sign of broken bones, "compressive neck injuries", significant cuts, or drugging or poisoning.
Former school caretaker Mr Huntley, 29, denies killing the 10-year-olds, who went missing in the Cambridgeshire town of Soham on 4 August last year.
However Mr Latham told jurors it was murder. "Ten-year-old girls don't just drop dead," he said.
Ian Huntley's ex-girlfriend Maxine Carr, 26, denies two charges of assisting an offender and one of conspiring to pervert the course of justice.
Mr Huntley was absent from court on Friday, the third and final day of the prosecution's opening speech, and Ms Carr sat alone in the dock.
No explanation was given for his absence, but on Thursday afternoon the court was told he was feeling unwell.
Earlier in the day, Mr Latham outlined details of how Holly and Jessica's badly decomposed bodies were discovered by walkers in a ditch about half an hour's drive from Soham.
They had apparently been dumped there within 12 hours of death, the prosecution alleged, and their remains later set on fire.
The forensic evidence against Mr Huntley was also outlined, including the discovery of fibres from the girls' Manchester United shirts on Mr Huntley's clothes.
Drawing his opening statement to a close in the afternoon, Mr Latham said that to convict Mr Huntley of murder, the jury had to be convinced of an intent to kill or cause serious harm.
The barrister said the defence may try to suggest the deaths were an accident. "We pose this question, two of them?"
"These were not two little babies. They were two fit 10-year-old girls," he said.
Mr Latham said the defence may also try to argue Mr Huntley had been "confused".
In that case they would have to consider his behaviour over the fortnight between the girls' disappearance and their bodies being found, he said.
Mr Latham said that Mr Huntley's former girlfriend, Maxine
Carr, had conspired to cover up the crime.
He said "as surely as night follows day" Ms Carr and Mr Huntley were working together to make a false story.
The court heard that after Ms Carr's arrest, she admitted she had been lying throughout the fortnight since the girls disappeared.
Ms Carr had explained this lie by saying Mr Huntley had been falsely accused of a crime in the past - before she met him - and she did not want that to happen again, Mr Latham said.
He said Ms Carr's motive for telling lies was irrelevant when it came to the charge of perverting the course of justice.
But Mr Latham said Ms Carr could only be guilty of knowingly assisting an offender if Mr Huntley was convicted, and if the jury believed Ms Carr knew he was the killer.
"It is her state of mind that matters. She has always strenuously denied that
she believed he was the killer," he said.
At the end of the day, Mr Latham explained to the jury that they would be visiting various relevant locations in Soham next week.
Killed and dumped
Earlier, as Mr Latham outlined the discovery of Holly and Jessica's bodies, on Saturday 17 August, he said the area - near Lakenheath in Suffolk - was well known to Mr Huntley, whose father had lived there.
Evidence suggested the girls' clothes had been cut off and their bodies set on fire after they were put in the ditch, he continued.
The bodies were so badly decomposed, and hidden in such a seldom-visited spot, they "may never have been found".
Both girls were still wearing necklaces. Jessica's was beaded and Holly's was metal with the word "love" inscribed on it.
Mr Latham said soil and pollen found in Mr Huntley's car matched those at the scene.
He said fibres from the girls' shirts were found on Mr Huntley's clothes, and fibres from items in the house were found on Jessica's shirt.
Earlier, Mr Latham described how police quickly decided to arrest Mr Huntley and Ms Carr, after finding the girls' clothes in a bin in a hangar at the school, Soham Village College, where Mr Huntley worked.
The arrests happened shortly before 0430 on 17 August 2002 - by coincidence, the same day Holly and Jessica's bodies were found.
The case was adjourned until Monday.