The jury in the Clydach murder retrial has been told they will never forget what were described as the worst murders Wales has ever seen.
David Morris denies the 'massacre' of Mandy Power and her family
Mandy Power, 34, Katie, 10, Emily, eight, and Doris Dawson, 80, died at their home near Swansea in June 1999.
David Morris, 44, of Craig-cefn-parc, Swansea Valley denies the murders, at a re-trial at Newport Crown Court.
But in its summing up the prosecution said Mr Morris was a "violent, lying thug" who had killed the family.
Mr Morris' previous convictions for the murders were quashed on appeal and a re-trial began in May.
On Monday prosecution barrister Patrick Harrington QC, in his closing speech, told the jury that these were the worst murders even seen in Wales.
He said it was the "worst type of massacre" and that there was "carnage".
Mr Harrington said divorcee Mandy Power had been bludgeoned to death along with her with children - Katie, 10, and Emily, who was eight - and their grandmother, Doris Dawson, with more than 80 blows from an iron pole.
The prosecution said the case against Mr Morris rested on a gold neck chain found at the murder scene covered in Mandy Power's blood and that his account of how it got there was a lie which proved his guilt.
Mr Morris had lied about the chain belonging to him until days before his original trial in 2002, and that he had tailored his version of events to fit the evidence against him, said Mr Harrington.
The retrial heard Mr Morris say he left his chain at the house the day before the murder when he said he had sex with Mrs Power.
Mandy Power's two daughters and her mother died with her
But Mr Harrington told the jury that phone records from Mr Morris' flat showed he was not there.
"His final lying account of what had happened had been blown apart," he said.
Mr Harrington reminded the jury that on the night of the murders Mr Morris had been drinking heavily and taking amphetamines - a combination that made him violent.
He said he had been drinking in a pub 15 minutes from where the murders happened and that, according to one witness, he had called Mandy Power "evil".
Other witnesses said Mr Morris had been seen wearing a gold chain very similar to the one found at the murder scene.
Also on that night, said Mr Harrington, Mr Morris had heard his own girlfriend - who was one of Mandy Power's best friends - called a "slapper".
He said Mr Morris had gone to find out more about his own girlfriend from Ms Power - and when he did not get information about her affairs with other men, he attacked her.
Mr Harrington said Mandy Power's daughters may have sprung to their mother's defence and that Mr Morris's anger then turned on them and their grandmother.
"Katie and Emily were total innocents who were brutally put to death," Mr Harrington told the jury.
He said: "The person who did that was not normal - was someone with a reactive temper which could not be kept under control".
Concluding his case, Mr Harrington said everyone who works in the court system can become immune to man's inhumanity to man
But he said no one involved in this case will ever forget it and turned to the jury saying "Neither will you".
The defence case will be summed up on Tuesday.