A year after the families of Helen Scott and Christine Eadie were devastated by the collapse of the case against their daughters' alleged killer, Tom Wood has published his long-awaited book about the case.

In it the former deputy chief constable of Lothian and Borders Police casts new light on the controversial decisions that resulted in the acquittal of Angus Sinclair, and reveals new details about the violent past of the man who could be Scotland's most prolific serial killer.

Wood also condemns as "archaic" and "unfair" a justice system that has allowed the balance of fairness to swing "very much in favour of the accused and away from the victim and public interest".

He concludes: "Many fundamentals of our law date back to a time when capital punishment meant there were lives at stake. We are out of balance.

"The public interest is poorly served compared to the interests of the accused. Our system failed to deliver justice for Helen, Christine and their families, and it afforded a hiding place to a mass rapist and killer."

The World's End – A Thirty-Year Quest For Justice will be on the shelves later this month, 31 years after the deaths of Helen Scott and Christine Eadie, both 17, who were killed after a night at the World's End pub in Edinburgh on October 15, 1977.

Co-written with the journalist and broadcaster David Johnston, the book is far from typical of a policeman's memoir.

Wood, who retired in the final stages of the World's End inquiry, concentrates largely on the efforts over three decades of many police officers of all ranks to deliver justice for the devastated families.

His awareness of the lasting effects of the murders on the families of the girls is apparent throughout and he said last night: "We often forget the ongoing nature of victimisation.

"We think of the victims as being the deceased. But when the families of Helen and Christine gave evidence last year, their wounds were still open and fresh after 30 years, and sadly they did not get justice."

The case against Sinclair was controversially thrown out in September last year by Lord Clarke, who accepted a defence submission of no case to answer after the Crown had completed its case. The strategy of the prosecution in cutting the case down to just nine days when six weeks' court time had been allocated, and in particular in leaving out crucial and damning evidence, has attracted criticism. Lord Advocate Elish Angiolini suggested the omissions would have made no difference.

The case finally reached court thanks to advances in DNA technology and painstaking detective work which revealed that semen from both bodies and from clothing at the scene belonged to Sinclair and to his late brother-in-law, Gordon Hamilton. Sinclair was already serving life for murder, rapes and sexual assaults on children.

The prosecution also managed to get DNA evidence from the ligatures used to bind the girls. This pointed to Sinclair and Hamilton, but was not used in court.

Detectives produced a time-line of the events of the night, which included reports from pathologists showing that Helen and Christine, whose bodies were found at separate points in East Lothian, had died soon after they were last seen leaving the pub. The Crown also failed to use the time-line.

Wood writes: "This led the judge to conclude that the girls could have been killed at any time up until the discovery of their bodies – some 15 to 19 hours after they were last seen.

He also notes that the Crown's reliance on DNA only from the semen samples enabled the defence to neutralise its impact by claiming Sinclair had consensual sex with the girls, something Wood describes as a "hateful suggestion".

He adds: "Amazingly, the special defence and the claim of consensual sex were seen to neutralise the DNA evidence.

"This we found unbelievable. Two young women had been found gagged, bound, raped and murdered and the man whose semen is found in them lodges an implausible defence of consent, which is accepted without question. It frankly beggared belief."

Wood said he was motivated to write the book as a memorial to Sinclair's victims, especially Helen and Christine, and to the dedication and unstinting effort of many police officers.

But he also hoped to get the message across that Scotland's justice system was out of balance.

'The World's End Murders – A Thirty-Year Quest for Justice' is published by Birlinn at £9.99. All Wood's proceeds from sales go to Victim Support Scotland.