He helped bring the World's End murderer to justice, prosecuted Peter Tobin for the death of Vicky Hamilton, and believes there is a "realistic possibility" a second trial could take place over Lockerbie.

Frank Mulholland swept in as Lord Advocate in 2011 with simple yet effective changes from the geography-based system and a view to make Scotland's prosecution service "much more professional".

With specialist working units leading to improved conviction rates across the country, in March this year he announced his decision to step down as Lord Advocate saying it was an "honour" to serve as Scotland's chief law officer for five years.

His half-decade in office has not been a quiet one with several high profile cases dominating Scottish headlines in each year; some holding a deeper personal connection to the public and Mulholland himself.

Even the way cases are managed and evidence is examined has changed during the 57-year-old's time since succeeding Elish Angiolini following the 2011 Scottish election.

Mulholland began his journey to the role of chief public prosecutor growing up in Coatbridge, Lanarkshire, before attending Aberdeen University where he graduated in 1981.

Three years later he was appointed a procurator fiscal depute in Greenock before moving on to work in Glasgow and Edinburgh.

He then became the first Advocate Depute to be appointed from within the Procurator Fiscal Service in 1997 before returning to the service in a number of roles:

(source: Scottish Government)

It was in this last position that Mulholland came up against one of his most famous cases, building-up the trial against Angus Sinclair in the World's End murders which collapsed due to "insufficient evidence".

After being appointed Solicitor General in 2007 and taking on the Lord Advocate role four years later, the World's End murders would be revisited in 2014 with Mulholland in a greater position of power and with improved technology on his side.

In a new interview with STV News chief reporter David Cowan, Mulholland said: "A number of persons have said to me I was under pressure. I certainly didn't feel it at the time but looking back on it, that's a fair comment.

"It was a huge amount of pressure given what happened in 2007 at the first trial, but that has never bothered me.

"It was personal in the sense that I knew the families, I knew the persons affected by it, the police officers who investigated it and the prosecutor who dealt with the case in 2007.

"I took the view as Lord Advocate there are certain cases you have to step up to the plate and deal with yourself. I suppose you wouldn't put another person through the onus, worry, focus or real pressure of that particular case. That had to be dealt with by the Lord Advocate.

In terms of advancing technology, he added: "DNA is now so sensitive, it's almost too sensitive. It will certainly be much more difficult [to get away with murder] than in the past when you didn't have DNA and cutting edge forensic science.

"That has been the one thing that in my time has seen an expediential rise in. I was involved in Scotland's first DNA homicide which was the murder of a young girl Christine Lee, aged eight in Castlemilk in 1990."

The outgoing law officer also referred to some other high profile cases he has covered in his legal career.

In his time as Solicitor General, Mulholland dealt with another high-profile murder case that gripped the nation and shocked many.

Mulholland's prosecution helped connect the properties where Tobin stayed in 1991 at Bathgate around the time of Vicky Hamilton's disappearance and the subsequent find of her remains in Margate where another teenage girl had gone missing.

Eyewitnesses said Tobin looked suspicious when staying at the Scottish house and searches on the property found a blade which bore traces of Ms Hamilton's DNA, while the girl's purse was found in St Andrew's Square with his son Daniel's DNA on it.

Tobin was given a life sentence on top of the life sentence he was already serving for the murder of Angelika Kluk.

During his time as Senior Advocate Depute Mulholland also successfully prosecuted the case against gas company Transco.

In December 1999 a gas explosion at a house in Larkhall caused a family of four to lose their lives. Andrew and Janette Findlay died in the explosion along with 13-year-old Stacy and 11-year-old Daryl.

In a case the first of its kind for Scotland, the Advocate's office took on Transco in the first ever prosecution for culpable homicide against a public limited company.

Transco were prosecuted for the lack of regard in health and safety and fined a UK record £15m.

Around the same time of the Larkhall home explosion in December 1999, college lecturer William Beggs murdered and dismembered the body of 18-year-old Barry Wallace after a staff Christmas party in Kilmarnock.

The "serial killer in the making" disposed of body parts of the teenage victim in Loch Lomond and in the sea off the Ayrshire coast but, by chance, Mr Wallace's remains were found during a training exercise by police divers in Loch Lomond. His head washed up on a beach in Troon after Beggs tried to dispose of it on a ferry.

Despite attempts to flee to the Netherlands Beggs was brought back to Scotland to stand trial, with Mulholland again involved in work around the trial as a jury found the Northern Irishman guilty of the brutal sex attack and murder.

Beggs was ordered to serve a minimum term of 20 years which, according to the judicial review action, is due to expire in 2019.

The Lord Advocate was also asked about the search for missing Moira Anderson in a search which has gone on for nearly six decades. Mr Mulholland revealed experts are offering their services to help two searches which will be carried out later in the year.

He told STV News: "It goes back to a family holiday I had in Australia where I have relatives. While I was there I took the opportunity to speak to Moira Anderson's sister.

"She asked me if I wouldn't close the file and do what we could to find her remains. And I thought that was a reasonable request and I agreed to that.

"We've been doing a lot of work in the last 12-18 months to narrow the search down to two particular areas which are rooted in the case.

"I think there is a prospect of success and nothing would please me more than to find Moira Anderson's remains. That would be a good ending to an appalling event."

Mulholland also reiterated a fatal accident inquiry into the Clutha helicopter crash is still on the agenda, but admitted it was a long process which required a specialised unit.

While Mulholland admitted he would watch any new legal developments "from the sidelines with interest" there will be some cases that have been left unclosed in his time as Lord Advocate.

In the interview with our chief reporter he discussed the prospect of fresh prosecutions over the Lockerbie bombing which caused the deaths of 270 people.

Last October, it was announced the lord advocate and the US attorney general had agreed there was "a proper basis in law" to treat the two Libyans as suspects.

Asked if there was any realistic possibility of them being surrendered for trial, Mulholland replied: "Before I embarked on this work I was told that there was no possibility, absolutely none, of the Libyans cooperating with law enforcement in Scotland or the United States. That happened.

"In 2011, I attended a ceremony in Arlington where the Libyan ambassador to the US made a public commitment on behalf of the Libyan government to help. They have kept their word. They have helped.

"I said it takes time, and it will take time, and that's certainly something which we are used to in relation to the Lockerbie inquiry.

"If we get to the stage of seeking the extradition of two named individuals or indeed more pe rsons, I think there's a realistic possibility that there could be a further trial."