Hong Kong-based blogger Cathy Odgers, ruled by Chisholm to have been part of a campaign to undermine Adam Feeley, was allowed to provide a "very detailed" written declaration in lieu of interview.
And former Hanover boss Mark Hotchin, despite his offer to talk from overseas via video link, was also not interviewed. At the time of the email the SFO was investigating Hanover, and the investigation was eventually dropped with no charges laid.
"While in an indirect sense Mr Hotchin's brief led to Mr Slater and Ms Odgers (and to a lesser extend Mr Graham) becoming involved in an attack upon Mr Feeley, the evidence does not justify the conclusion that Mr Hotchin was actively involved," Chisholm said in his report. Mr Hotchin's employee Kerry Finnigan was similarly excused.
(Disclosure: This reporter, who broke the story leading to Ms Collins' resignation, was also not interviewed for the inquiry.)
What information wasn't considered?
While Ms Collins allowed clones to be made of her laptop, phones and an iPad and the data assessed by KPMG, these were found to contain "very little in the way of relevant or potentially relevant material," Justice Chisholm said.
Ms Collins was also unable to provide the Inquiry access to her Facebook communications, as she said her account had been deleted in 2013. Parliamentary services landline data was also not available.
And while Ms Collins' mobile phone records showed a number of calls to Slater, they showed none from Slater to her.
"The absence of telephone records for Mr Slater's calls is surprising given that both Ms Collins and Mr Slater confirmed that they phoned each other often," Justice Chisholm said.
Who was Slater working for?
Slater told the inquiry he first began working for Mr Hotchin to set up a website, but over time his role evolved into public relations defending the embattled financier. "The value that we got is that we managed to shunt [Hotchin] off the front pages of the papers," Slater told Justice Chisholm of his efforts.
Odgers told the inquiry she was recruited by Graham, then-spokesman for the former Hanover boss, in February 2011 to "provide online media support for Mr Hotchin and to advise on a strategy to counter his treatment in the media".
Graham said he "engaged" the pair to try "telling Mr Hotchin's side of the story".
Both Slater and Odgers said their work for Mr Hotchin had ceased by mid-2012.
Emails obtained by the hacker Rawshark appear to show both Odgers and Slater were paid for their work for Mr Hotchin.
What happened to the police complaints?
In the aftermath of Ms Collins' resignation, then-Labour Party deputy leader David Parker wrote to police requesting, amongst other complains about the Dirty Politics saga, an investigation into the possibility that the public relations campaign on behalf of Mr Hotchin amounted to perverting the course of justice.
When the Chisholm inquiry began summoning witnesses, Slater, Odgers and Graham tried using Mr Parker's complaint to suspend the Inquiry, arguing the probe into Ms Collins could prejudice any police investigation.
But police confirmed on October 15, mid-way through the inquiry, that the matter had been shelved "subject to the reservation that the matter might be reconsidered if any substantive evidence was subsequently provided".
A key email underpinning Mr Parker's complaint - an email from Graham appearing to show Hotchin instructed Slater and Odgers to smear a possible witness in the SFO investigation - was ruled by Chisholm as "beyond the scope of the inquiry" and not considered.
