Police Scotland’s Chief Constable has insisted erecting a forensic tent in Nicola Sturgeon’s garden was “proportionate and necessary”.
The move was part of the investigation into the SNP’s finances, which Sir Iain Livingstone said had “moved beyond” initial reports.
Ms Sturgeon was arrested in June and questioned for more than seven hours before being released without charge.
She has said she is certain she has done nothing wrong.
Police Scotland has been investigating what happened to more than £600,000 of donations given to the SNP by independence activists since 2021.
In April, police arrested Ms Sturgeon’s husband Peter Murrell, the SNP’s former chief executive, before he was released without charge pending further investigation.
As part of the operation, a tent was put up in the garden as various items were removed from their Glasgow home.
Ch Con Livingstone told BBC Radio’s Today programme he would have “rightly been accused of a significant dereliction and neglect of duty” if Police Scotland had not carried out its investigations the way it had.
He said: “I know the full circumstances of the case. 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.”
As part of the probe, known as Operation Branchform, officers searched the SNP’s headquarters in Edinburgh in April.
A luxury motorhome, costing about £110,000, was also seized by police from outside the home of Mr Murrell’s mother in Dunfermline.
Almost two weeks later, SNP treasurer Colin Beattie was also arrested and released without charge while further inquiries were carried out.
Mr Beattie resigned as party treasurer shortly afterwards.
Ms Sturgeon, Mr Murrell and Mr Beattie were the three signatories on the SNP’s accounts.
Sir Iain Livingstone, who is to retire later this summer, has previously defended Police Scotland’s investigation and said he would “fiercely resist” any political interference.
He also urged politicians and members of the public against speculating on the probe, which continues.
He told the Today programme that Operation Branchform, like other investigations into the finances of an organisation, had been “complex” and would take time.
He said: “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.”
‘We’ve done the right thing’
He added: “There’s been a prudent, thorough and proportionate investigation carried out. It’s 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.
“We’ve done the right thing, that the rule of law and interest of justice must prevail.”
Ms Sturgeon announced on 15 February – four months before her arrest – that she would be standing down as both SNP leader and first minister once a successor was elected. Humza Yousaf later won the contest to replace her.
She said at the time that she knew “in my head and in my heart” that it was the right time to go, and has since denied the timing was influenced by the police investigation.
Commenting on the Chief Constable’s latest remarks to the BBC, First Minister Humza Yousaf said: “Obviously the comments Sir Iain Livingstone made are on behalf of Police Scotland and it is very much an operational matter for Police Scotland.
“All I can say is that the SNP will continue to do what we’ve done from day one and that’s fully co-operate with any police investigation.”
Scottish Conservative party chairman Craig Hoy said confirmation that the investigation into the SNP’s finances had moved beyond the initial complaint “only highlights the seriousness of this investigation”.
Scottish Labour’s deputy leader Jackie Baillie said: “From what was a single complaint, it now appears that there are multiple lines of inquiry and a can of worms has opened up.”