SNP chief Peter Murrell is alleged to have sent messages that suggest 'pressurising' police over the Alex Salmond case.
Convener Linda Fabiani said the committee is 'completely frustrated with the lack of evidence' it has received.
Scotland's top civil servant Leslie Evans is due to give evidence before MSPs in Tuesday's opening session.
Potential witnesses in Holyrood's inquiry include Nicola Sturgeon, her husband Peter Murrell and Alex Salmond.
