Justin Cotta dives into Sweeney Todd's heart of darkness

What should the Demon Barber of Fleet Street sound like when he sings? Like one of the Horseman of the Apocalypse, says Justin Cotta, the actor charged with bringing a killer to life in the New Theatre's upcoming production of Stephen Sondheim's musical thriller Sweeney Todd.

"I don't want to impose anything artificial on the character but I've got to get to the heart of him," Cotta says. "It's one of those roles where you have to risk absolute failure and embarrassment to even have a crack at pulling it off. You can't tiptoe into it. You have to go right out on a limb to even get close to what Sondheim demands of you. That's terrifying for a performer, and that's why you say yes to doing it."

Sweeney Todd is Cotta's first "proper" musical theatre role, he says, but he's no newcomer when it comes to singing to a crowd. Cotta was the lead singer of the short-lived hard rock band Memento, an outfit that managed to crack the US rock charts in 2003. He's also a past member of Seattle industrial-rockers V.A.S.T.

"That style of singing has been my bread and butter for 10 years but to do Sweeney Todd, you need to find more colour and expressiveness," says Cotta. "I didn't want to do a contemporary rock Sweeney. I wanted to honour the Shakespearian scope of it, the blood and guts and soul in the writing. I didn't want Sweeney to come to me, I wanted to go to him."

Written in the late 1970s, Sweeney Todd is the darkest of Stephen Sondheim's musicals. Set in the grim backstreets of mid-19th century London, it tells the story of Benjamin Barker, who returns from 15 years of penal servitude in Tasmania to wreak a terrible revenge on the corrupt judge who sent him there.

Sweeney's experience in Australia is key to understanding his mind and actions, says Giles Gartrell-Mills, the production's director. "It's the old adage: you have to go to prison to learn how to become a criminal," he says. "Sweeney is a creation of the penal system in Australia in the 1800s. He embodies all that incredible brutality and it's what drives the play."

And there's darker stuff besides, adds Cotta. "Sondheim had a terrible relationship with his mother," says Cotta. "On her death, apparently, she managed to scribble some lines to him that went something like, 'My only regret in life is that you were born'. That kind of pain is in Sweeney, too."

Sweeney Todd is Sondheim at the peak of his powers, Cotta says, written at a time when the theatre industry – only half jokingly – had taken to calling him "God".

"You can hear an arrogance in it as he hacks away at industry, at capitalism and at criticism. I think there's something personal in Sweeney's desire for vengeance," Cotta says.