A promising young firefighter  accused of arson in a recent string of fires in Mayerthorpe, Alta., including one that destroyed a historic CN trestle bridge last week, is due to make his first court appearance Wednesday.

Many in the town of 1,400 are expressing shock and a sense of betrayal over the weekend arrest of Lawson Michael Schalm, 19.

Mayerthorpe RCMP said tips from the public led investigators to arrest Schalm and lay 18 charges against him.

Shalm is the son of Albert Schalm, the town’s former mayor. The elder Schalm told CTV Edmonton he learned of his son’s arrest through social media and was in “total shock.”

He said he was struggling to deal with the news, and while he hasn’t been able to speak to his son yet, he supported him with unconditional love.

“Lawson will always have a place at my table. I will never throw him under a bus,” he said.

Fire chief Randy Schroeder said his department didn't see Schalm's arrest coming. He said Schalm started as a volunteer cadet at age 15, became an eligible firefighter on his 18th birthday, and was destined to be a longstanding member of the department.

He said members of the department are feeling “a certain sense of betrayal,” hearing that one of their own may have been responsible for the fires.

Schalm was an active firefighter at five of the fires and was a bystander at another four at least, said Schroeder.

He added he attributed recent changes in Schalm’s behaviour to him growing up, but declined to offer specifics.

“I try not to take it personally. I’m struggling, like a lot of our members, with ‘why’ and ‘how’ and ‘what did we miss?’” he said. “I’d like to be able to roll the tape back, metaphorically speaking, and get a better understanding.”

He said fighting and investigating the recent rash of fires has been hard on his department, noting that firefighters responded to five fires on Friday alone.

“At the height of this [past] week, we were running calls an hour to an hour and a half apart. With the trestle [bridge fire] we were 12 to 14 hours on that scene,” he said.

The wooden bridge was destroyed last Tuesday in a spectacular blaze that led to the evacuation of two schools and a trailer park. It took three dozen firefighters from four departments, helicopters and a water bomber to douse the flames.

Mayor Kate Patrick said the community is grateful an arrest has been made but saddened it was someone well known.

“It’s a sad day but it’s a relieving day for the community that someone has been apprehended,” Patrick told CTV News.

Patrick described the family as a “well-respected and very nice family” and she urged the community to support them.

Schalm will remain in custody until his first court appearance in Stony Plain Provincial Court on May 4.

With files from CTV Edmonton’s Breanna Karstens Smith