The seizing a PC's etc is more to do with recent documents that'll still be present on the PC. The file may have gone, but the draft word file entitled "FAO Hein; I think we need to urgently discuss the dossier" would still be in the recently cached folder. Had any of the recent revelations about a whole host of allegations riled McQuaid, then there would be the record of McQuid searching for specific information, emails transactions between himself and any other parties of interest etc. From this information (or even the meta data - email addresses and time of emails or phone calls, not the content itself), a good forensics team can piece together what actions may have been taken.
For an example, McQ may have had an email from a certain contact, then immediately checked an account through online banking, then called another contact. You may not know the content of the email, the amount in the account or the content of the phone conversation, but the pattern (was this a single event or a monthly event?) would help build a picture.