The police investigation into the funding and finances of the SNP has expanded to look at “potential embezzlement”, the Chief Constable of Police Scotland has suggested.
All three have been questioned by officers investigating the party’s funding and finances, before being released without charge pending further inquiries.
Ms Sturgeon has insisted she is “innocent of any wrongdoing” and has “committed no offence”, describing her arrest as “both a shock and deeply distressing”.
Appearing on the BBC’s Today programme on Wednesday, Sir Iain was asked why the investigation – which was formally launched two years ago – was taking so long.
In his reply, he suggested that it had become increasingly complex as officers examined not just the SNP’s finances but other connected matters.
“Investigations into the finances of an organisation, the finances of an individual, are often complex,” he said.
“Investigations around fraud or investigations around potential embezzlement or investigations around the misuse of funds take time.
“You need to go and obtain information from banks and other financial institutions. We can’t just do that automatically.
“We need to go and seek judicial warrants for that. There needs to be a process around that.
“So the time that’s been taken, in my judgement, is absolutely necessary.
“There’s been a prudent, thorough and proportionate investigation carried out. I have been aware of this investigation since the outset.
“It has got a dedicated team of specialists who are involved in it and they are working very closely with our prosecutors, the Crown Office in Scotland, in terms of the steps that are taken.
“What I would say is that had we not carried out this investigation in the manner we have, I would rightly have been accused of a significant dereliction and neglect of duty.
“That’s not the case. We’ve done the right thing. The rule of law and the interests of justice must prevail.”
Asked whether the investigation had expanded from the original allegation – that funds raised to support efforts to secure a second independence referendum had been spent on other things instead – Sir Iain confirmed that this was the case.
“It’s moved beyond what some of the initial reports were, and that’s not uncommon in investigations such as this,” he said.
The Chief Constable also defended the police’s controversial decision to erect a forensic tent in front of Ms Sturgeon and Mr Murrell’s house in Glasgow.
“It absolutely was [proportionate] given the circumstances of that search,” he said. “The tent was there, as were all the other measures, to protect the interests of justice and to protect the individuals involved. So it was a proportionate and necessary step.”
Asked when the investigation was expected to conclude, he said: “I can’t put any absolute timeframe on it, but matters will progress in a proportionate and timeous manner.”
The SNP was approached for comment.