Ex-Bill star Walkinshaw revealed that the PE teacher is the prime suspect in the hit-and-run on headmaster Michael Byrne (Alec Newman).
"Since Michael's hit and run all fingers are pointed at Jez," he told What's on TV. He feels under a lot of pressure and is very frustrated.
"Everyone he works with at school sees him as the main suspect. He thinks they should come out and say it instead of gossiping behind his back."
Explaining why Jez will continue to lie about his alibi, the actor said: "He told Sian (Jaye Jacobs) he was at the gym, as he doesn't want her to know he was at Janeece's apologising for a drunken pass he made at her! Even though it was innocent he wants to draw a line under the whole thing and move on by making his marriage his priority."
Asked why Jez is so keen to return to Waterloo Road, Walkinshaw added: "He goes back to work because he wants to see for himself that the affair between Michael and Sian is over.
"He also comes back to prove a point to Michael that he's the bigger man. Jez thinks 'I'm going to be professional, but I'm also keeping my beady eye on you Michael!' There's definitely trust issues at play for Jez."
Waterloo Road returns next Wednesday (February 22) at 7.30pm on BBC One.
> Spoiler: Waterloo Road is infiltrated by a gang
> Read more Waterloo Road news and spoilers