Bone fragments from a child and blood matching missing five-year-old April Jones were found in the home of a man accused of murdering her in a sexually motivated attack, a jury has heard.
April went missing near her home in Machynlleth, Powys on 1 October 2012.
Mark Bridger, 47, of nearby Ceinws, denies abducting and murdering April.
The jury was shown what the prosecution called "very unpleasant" images from Mr Bridger's computer.
Mr Bridger also denies intending to pervert the course of justice.
Opening the case for the prosecution, Elwen Evans QC, said the defendant had gone to enormous lengths to conceal what he had done.
"He has played a cruel game in pretending not to know what he has done to her and with her. It is a game to try and save himself," she said.
The jury heard Mr Bridger undertook an "extensive clean-up operation" at his home which included the disposal of April's body and her clothes.
However, some evidence remained. Blood found in the living room, hallway and bathroom matched April's DNA.
Ms Evans told the court that bone fragments found in fire ashes at his home were consistent with those of a juvenile human skull, according to experts.
A concentration of blood was found near the wood burner at Mr Bridger's home. Around the wood burner were a number of knives, one of which was badly burned.
"The defendant was an experienced slaughter man who knew how to use knives professionally," she explained.
Ms Evans said April was last seen on 1 October last year "happy and smiling" getting into the defendant's Land Rover.
"He drove her away and that was the last that anyone apart from the defendant saw of April."
She added: "The largest search in British policing history has failed to find her."
The prosecution said Mr Bridger claimed he was involved in a road traffic accident with April, then put her in a car to get her medical attention "although he did not in fact approach anyone for help".
He claimed he drove around Machynlleth, an account which the prosecution said was undermined by the evidence, including CCTV.
He said there came a time when he was driving around when he had no recollection of what happened.
Mr Bridger also said he was too drunk to remember but he believed he put her somewhere out of the rain.
He denied taking her to his home and said he did not sexually abuse her.
Mr Bridger had claimed he ran over April and she was "pinned under the front tyre" of his Land Rover. He claimed he tried to give her mouth-to-mouth resuscitation and drove away to get medical help.
However the prosecution said April's friend remembered Mr Bridger standing "as though he was waiting for someone".
The friend said when April went to the car "the man did not carry her into the car. April got in herself, by herself" and was described as "smiling".
Mr Bridger spent a lot of time outdoors participating in what he called survival and bush craft.
He claimed to know the "rugged terrain" around Machynlleth well.
This played a significant feature in the police deciding the size and scope of their search for April, the jury was told.
The defendant told people he had had a career in the armed services, including the SAS, but the prosecution said military records showed any army career was "a lie, a fantasy".
Mr Bridger worked in an abattoir from 2009 to 2012. In October last year he was working as a labourer in a guest house which was being renovated.
The jury was told Mr Bridger's computer contained images of child sex abuse as well as photographs of local children. His computer records also showed he had an interest in child murder cases.
Search terms Mr Bridger used on his computer included "naked young five year old girls" and "nudism five-year-old".
He had images of high-profile murder cases, including the Soham victims Holly Wells and Jessica Chapman on his computer.
Later, the public gallery was cleared while jury members were shown images but April's parents asked to stay while the evidence was being viewed.
The prosecution warned the jury some of the images were "very unpleasant, but we say it is highly relevant".
They heard evidence of three folders on Mr Bridger's computer. Two were titled with girls' names and another called "ZO" where most of the indecent material was located.
The jurors were reminded that the trial must be decided on the evidence and they must not let feelings of "taste" or "disgust" cloud their judgement.
Ms Evans told the jury the prosecution did not have to prove a motive, adding: "This is a case where the evidence, we say, clearly indicates a sexual motive, and you cannot realistically assess the facts, we say, without knowing what interests the defendant."
They were also played the 999 call made to report April's disappearance, where a woman's voice can be heard saying: "My daughter's been kidnapped".
April's mother Coral could be heard sobbing loudly in the background during the call.
In the 999 call played to the jury, the operator is told there was a "big grey car and a man driving". A voice was heard shouting: "Someone's kidnapped April."
The defendant wiped a tear from his eye as the 999 call was played.
Mrs Jones and her husband Paul were seated in the front row of the public gallery throughout the morning's proceedings.
Both were wearing pink ribbons, which became the symbol of the search for their missing daughter following her disappearance.
The trial heard April had a relatively mild form of cerebral palsy "but that did not stop her leading a full and active life".
She had been "out and about" and swimming at the local leisure centre on the day she disappeared.
Earlier, Ms Evans warned the jury warned that the case was "likely to provoke strong emotions".
She told them they must decide the case "fairly and squarely on the evidence you hear".
Mr Bridger remained staring straight ahead as the case was outlined against him. He was wearing headphones to ensure he could hear everything said in court.
The trial, which could last until the middle of June, was adjourned until Wednesday.