In the first part of a two-day interview, the new head of the PSNI’s Serious Crime Branch, Detective Chief Superintendent Derek Williamson talks to Crime Correspondent Deborah McAleese about his team’s hunt for Northern Ireland’s most dangerous offenders

Last month a 44-year-old man was convicted of throttling his elderly neighbour to death — 20 years after the murder.

For almost two decades William James Stevenson was the chief suspect in the murder of 66-year-old Lily Smyth, however there was never enough evidence to charge him until DNA advances eventually linked him to the horrific crime.

The conviction of Stevenson was the result of years of dedication and hard work by detectives in the PSNI’s Serious Crime branch and the Historical Enquiries Team and offers hope to the victims of many unsolved crimes.

Detective Chief Superintendent Derek Williamson has just taken over as head of Serious Crime Branch and he believes that future breakthroughs in forensics will help lead to convictions in many other unsolved crimes.

“Stevenson was always under suspicion but the difficulty was that we never had the forensic evidence to take us over that line towards a prosecution,” he said.

“It was a result of a review of the case and development around DNA techniques that pushed it |over the line.

“The message that comes out of that case is that I would never tell a family a case is closed because there is always the possibility that new forensic techniques will be developed or that |someone takes a pang of guilt and comes forward.”

Mr Williamson also said there there are a few cases at the moment where new forensic evidence and techniques could be brought to bear.

He said: “But we could still bring old cases forward without forensics.

“The most successful cases are those when the public come forward with information and support us with actual statements.”

More than 300 police staff work within the PSNI’s Serious Crime Branch, which investigates a range of serious crimes including murders, stranger rape, images of child abuse, kidnaps and internet crime.

Last year, 20 homicide investigations were under way within the branch.

Its rape crime unit, which deals with stranger rape, is currently running 250 cases.

And in recent months the branch has launched a number of conspiracy to murder investigations.

“This type of crime (conspiracy to murder) is very much under the radar and the public is not very aware of it,” he said.

“We have spent a lot of time in recent months on a number of these investigations.

“We have received evidence or intelligence that a murder is in the planning and a huge amount of resources are used to make sure it does not happen and to gain evidence of who is involved to bring them before the courts.

“This type of crime is more difficult to investigate than murders as you are basing your investigation around a clandestine plot.”

Although the PSNI’s investigative powers came under scrutiny last year following the failure of three high profile cases — the Omagh bomb, Northern Bank and Robert McCartney murder trials — the Serious Crime Branch had successful outcomes in a large number of cases.

TOMORROW: Regrets over the failed Omagh bomb trial; the Robert McCartney murder; the Northern Bank robbery