Alan Marshall said he hoped some good would come from the trial.
"We are not required to be there and we're not witnesses at all ... but obviously it's all just part of our journey. We will be there to honour Andy and put a few things to bed, I guess, in terms of just understanding what happened."
The family know little about the circumstances of Andy Marshall's death.
It is understood Schmidt has lived in New Zealand, although a West Australian police spokeswoman said he and Andy Marshall were not known to each other before the night Mr Marshall died.
Said Alan Marshall: "We don't know the guy, we've never met him, we haven't even seen a photo of him ... I guess it'll be about letting the court process unfold and we'll just take each day as it comes."
The family were in close contact with a police liaison officer.
"We don't know how we are going to react, as we are going to end up in the same room as him, so you don't really know how that's going to go ... but it's all part of facing the harsh realities and I think it's an important thing to do."
Alan Marshall said life had not grown any easier since his son's death. "It's just a case of one day is the same as the next and we have to function in practical ways, but it's never far from you and it certainly doesn't improve.
"But in a lot of ways you don't expect it to - it's your son, nothing changes and nothing will bring Andy back.
"So you live through that every day and it's been the stuff, as a parent, your worst nightmares are made of ... You learn to manage it, rather than any of it going away."
Looking to the trial, Alan Marshall hoped for the facts to come out.
"I don't think we would call it closure, but you want the truth to come out and you want it to be dealt with accordingly."
