South Wales Police chief constable, Sir Anthony Burden, has responded to claims in a BBC Wales Panorama programme about the investigation into the 1999 Clydach murders.
Mandy Power, her two daughters Katie and Emily and her mother Doris Dawson, were beaten to death in a savage attack at their home, which was set alight to try to destroy forensic evidence.
The programme raised questions over the investigation into the deaths, revealing serious failures to follow up potentially vital leads.
Following the programme, Sir Anthony said: ""We are disappointed with the broadcasting of a programme that has clearly set out to undermine all the excellent work this force does in investigating major crime.
"Our decision not to take part in the Panorama programme was based on independent legal advice, which centred on the legal proceedings that are ongoing.
"We were not prepared to take the very real risk of undermining that legal process, simply so that we could defend our position.
"For the same reasons we cannot, at this time, respond in any detail to the allegations made against South Wales Police in the programme.
"I am sure the people of south Wales, and certainly the victims and their families who have already suffered enough tragedy, would not want to see justice potentially prejudiced by comments made by us to support our position."
He said the force may take the opportunity to respond in the future when the legal process "is no longer at risk".
The force had been "honest, professional and transparent" in reviewing and reinvestigating all unsolved and unresolved murder cases, according to Sir Anthony.
"We have worked very closely with the families, keeping them updated on every development, and we have used independent reviewers, with independent oversight at every stage," he said.
South Wales Police dealt with 356 murder investigations over 20 years, only five of which were miscarriages of justice, Sir Anthony added, saying not all were overturned due to the original police investigation.
"However, we fully accept that one case is one too many, and we take our commitment to dealing with the reviews very seriously and as a priority.
"We have already had significant successes in the cases of Geraldine Palk, the Llandarcy murders, Patricia Simpson and most recently, Lynette White, a case that we reviewed and reinvestigated.
"A conviction was secured, and we are now carrying out a detailed inquiry into the original investigation," he said.
"The very nature of such detailed re-examination of what are extremely complex investigations means that each takes a considerable amount of time.
"We have committed significant resources to the review programme and we will continue our commitment until it has been completed.
"At the same time we will continue to respond to today's serious crime investigations and will continue to do so professionally and effectively."