The Electoral Commission has defended the way it handled its inquiry into donations to Wendy Alexander's Scottish Labour leadership campaign.
Wendy Alexander was not reported to prosecutors
Speaking publicly for the first time about its decision not to refer Ms Alexander to prosecutors, the commission dismissed criticism.
It followed an investigation into an illegal £950 donation made to her campaign from a developer in Jersey.
Critics branded the process a whitewash but the commission said it was robust.
Head of the Electoral Commission in Scotland Andy O'Neill said the 10-week process had been necessary.
He said: "I actually personally don't think that was a particularly long time.
"You have to bear in mind there are other investigations which are still ongoing which haven't reported, yet started before this one.
"You simply can't say it will take a week or two weeks - you have to be robust and thorough, which is what we've tried to be."
Ms Alexander's leadership campaign team solicited a payment of £950 from Jersey-based businessman Paul Green.
The donation was illegal because it came from someone not on the electoral register.
The commission ruled Ms Alexander did not take all reasonable steps to comply with the law, but found she had taken "significant" steps.
The Scottish Labour leader said the decision had proven her "honesty and integrity".
In a wide-ranging interview on BBC Radio Scotland, Mr O'Neill also said the commission was in the process of setting standards for the design of election ballot papers in a bid to prevent a repeat of last year's Scottish election fiasco.
SNP MSP Roseanna Cunningham said: "Clearly the Electoral Commission want to justify their investigation into Wendy Alexander.
"The problem the commission now faces is that there is little faith left in its enforcement of the laws."
Ms Cunningham said there were still questions the commission needed to answer.
She said: "When is an illegal donation actually illegal? What will happen to anyone accepting, knowingly or otherwise, an illegal donation in the future?
"The commission may feel it acted properly in the investigation but the Wendy Alexander decision has created a black hole in our electoral laws."