The note was signed off by Ms Bain, according to a letter released on Tuesday.
The Scottish Tories lodged an urgent question in the Scottish Parliament on Wednesday urging the KC to confirm whether she had “misled” MSPs.
Ms Bain had sent a memo on January 19 notifying the First Minister about the case, informing him the case was active under the Contempt of Court Act 1981. It was thought this was the first time she had written to Mr Swinney about the legal details.
The KC has been urged to consider whether her dual role as chief prosecutor and a member of Mr Swinney’s cabinet as the principal legal adviser, is “tenable”.
Speaking in Holyrood, Ms Bain said she provided responses last week “with care based on information and documentation available to her at that time”.
She added: “I had not in the time available before answering the urgent question seen the March 2025 document.
“I had not seen the document since it was sent, nor any of the other examples, nor been given advice on the impact of proceedings if information were released.
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“I therefore undertook to consider the point in more detail and provide examples. It would have been quite wrong for me to answer such a sensitive issue, any live criminal case, with anything less than the fullest understanding and consequences of the issue.”
Ms Bain was repeatedly asked to clarify whether she had forgotten, or whether she did not know the memo had been sent in March last year.
She said: “Of course I saw the March 25 document when it was sent from my office but I did not see it before I entered the chamber to answer questions.”
She said she was “constrained” about what she could say on live proceedings.
She said: “I understand why people may feel uncomfortable with the First Minister… information that others do not. In a sensitive context, that might be heightened. But the reason the First Minister gets to know some things that the public do not is because he has responsibilities the public do not.
“I am here today as Lord Advocate. I discharge my duties in that office independently of any other person and independently of any political interference.”
She said she did not “brief political parties”.
The Lord Advocate, who has a dual role as the top prosecutor and a member of Mr Swinney’s cabinet, appealed to MSPs to show “common decency” after some accused her of refusing to answer questions.
John Swinney. (Image: Jeff J Mitchell/Getty Images)
Mr Kerr said: “The latest bombshell revelation about the Lord Advocate’s conduct in relation to the criminal case against Nicola Sturgeon’s husband reeks of scandal.
“We thought the public and the media had only been kept in the dark for a matter of weeks compared to when John Swinney knew, but we now know Swinney was given a secret update nearly a year ago by Scotland’s top law officer about this case.
“This is damning proof that the SNP’s justice system operates on two tiers. Serious questions remain as to why Dorothy Bain didn’t tell Parliament the whole truth about her shady briefings to Swinney when she was in Holyrood last week.
“That’s either a serious lapse in judgment or an outrageous example of SNP secrecy.
“This rotten episode which has seen the Lord Advocate give the SNP politically advantageous information must be the final nail in the coffin for her dual role.”
“Dorothy Bain had another opportunity to come clean in parliament today, but she refused to explain why she deemed it acceptable to tip off the SNP leader about the party’s former chief executive being charged.
“That’s a shameful dereliction of duty and she should seriously consider whether her position is tenable.”
Mr Swinney was questioned by LBC on why the March 2025 memo was not mentioned last week. He said the Lord Advocate had been “entirely open”.
He said it was “important” he was advised on important cases by the chief legal adviser.
Ms Bain also provided a list of almost 30 cases where the Lord Advocate has updated Scottish or UK Governments on over the last 30 years.