As part of the investigation into United Kingdom parliamentary expenses scandal, Thomas was found to have over claimed £349.20 in mortgage interest between 2004 and 2005 under the additional costs allowance (ACA). He was recommended to repay this sum.
Apparently no money was ever repaid.
On this day Thomas resigned as an AM, and from Plaid Cymru following his arrest by police on suspicion of possession of indecent images. His seat was taken by Helen Mary Jones, who was next in line on Plaid's regional list.
On the 18th September he was charged by Dyfed-Powys Police with three counts of making indecent images of children. In the context of digital media, saving an indecent image to a computer's hard drive is considered to be "making" the image, as it causes a copy to exist which did not exist before.
Thomas pleaded guilty to three counts of making indecent images at Aberystwyth Magistrates' Court on the 3rd October 2018, having made over 600 such images and videos.