Whoever killed Stephen Bain killed the rest of the family and a "volume" of evidence points to David Bain, the Crown says.
The Crown finished summing up its case against David Bain at his retrial in the High Court at Christchurch yesterday.
Crown prosecutor Kieran Raftery told the jury that they should focus on who killed Stephen Bain, as the same person killed Margaret, Arawa, Laniet and Robin Bain.
"Answer the question 'who killed Stephen?' and you've answered all five counts in this indictment," Mr Raftery said.
He said the blood found in Stephen Bain's room and the fact that he was strangled pointed to a violent struggle.
Stephen was shot three times, the first shot was likely to have wounded him in his hand, the next skimmed his scalp and the third was fatal, as it entered the brain after he was strangled and incapacitated.
Mr Raftery said Stephen was known to be able to fight his corner in the school playground.
He said the defence had described Robin as 58 going on 78 and, therefore, Robin was not the man who fought with Stephen.
"Of the two protagonists, Robin or David, who was the most likely one? We know from the scene he [Stephen] fought like hell to stay alive."
Mr Raftery put on the blood-stained gloves found in Stephen's room and lifted the rifle used to kill the Bain family on the morning of June 20, 1994.
He showed the jury how he believed David and Stephen's hands had come into contact with the rifle during the struggle. Mr Raftery told the jury that small samples of Stephen's blood were found on Bain's clothing.
"There is a volume of evidence that connects David Bain and David Bain alone with the murder scene in Stephen's room," Mr Raftery said.
The Crown also alleged that Bain used his paper round as an alibi and broke his routine at one house to make sure that he was noticed.
Mr Raftery said Bain took his dog with him on the morning and went inside the gate of one of the properties where he knew another dog would bark.
He said Bain told police the woman whose dog barked at him would remember seeing him.
"It is an essential part of his plan if he is to frame his father," Mr Raftery said.
Mr Raftery also told the jury that Bain did not act like a brother when he heard Laniet making gurgling sounds.
Bain told police he heard the gurgling noises from Laniet's bedroom after returning from his paper round.
"Does he behave like a brother? Does he go straight to the telephone and dial 111? He does no such thing for 20 minutes."
He asked the jury, if Bain heard signs of life, then why did he wait?
Mr Raftery described the scenario as "totally untenable" and called it a "Freudian slip" by Bain.
"He's talking about a time during the course of the murders that he was committing," Mr Raftery said.
He also questioned evidence that defence witnesses have given, suggesting that Laniet was having an incestuous relationship with Robin.
Mr Raftery said according to evidence given by a number of witnesses, Laniet had three babies before she was 12 years old.
Mr Raftery ended his summing up by recalling evidence from a friend of Bain who met him shortly after the killing. He quoted Bain telling the woman: "I always seem to end up hurting those that I love."
Mr Raftery finished the Crown's case by saying: "That is exactly what he has done in this case".
The defence begins its summing up today.