From counter-terrorism operative Tom Quinn in Spooks' first two seasons to the Sheriff of Nottingham in Ridley Scott's 2010 Robin Hood reboot, the 39-year-old has plenty of experience of portraying various upholders of the law. However, he cheerfully admits he could never take on such a vital assignment in real life. "With every role, you imaginatively jump into it and you think that you could be a soldier or a policeman," he says.
"You've got to believe in it and take it a little bit seriously. You get to dip your toe into something and often you meet people who actually do it for a job. When I made the film Incendiary, I got to hang out with a bomb disposal team who were there in Tavistock Square during the bus and tube bombings in London in 2005. So you have amazing insights into other professions and you can safely slip in and out of them."
With its frequent, unflinching depictions of violence, Ripper Street is certainly not for the fainthearted, although Rothenberg - who plays former Pinkerton agent and US army surgeon Captain Homer Jackson - insists that it comes with the territory.
"It's an integral part of the show as it is called Ripper Street after all," he laughs.
"It was a tough age so it has to be that violent and that hard. That's exactly what it is and I think that's great.
"Usually, with shows set in this time period, it's a comedy of manners or a story about the British class structure or people being repressed. That was maybe true for about 5 per cent of the population and this shows what everybody else was up to."
"When the first episode came out on TV, even I was like 'woah, that's dark!"' adds Flynn, who has also dealt with moments of considerable brutality in his role as the mercenary Bronn in Game of Thrones. "But it's just the violence that was around at the time."
Born in New Jersey, Rothenberg guested on popular US shows Law and Order, Person of Interest and Elementary before crossing the Atlantic to take his first regular role in Ripper Street. "It happened so fast that I didn't have time to go to medical school," he jokes, referring to his less-than-extensive research.
"But it did make me realise how far removed we are from everything nowadays as I couldn't tell you how anything actually works. I have no sense of how my phone or my computer works but back then people were much more hands-on.
"You could see how things worked as the average guy in the street could grow food to feed his family or he could fix his shoe. So it made me understand the world that I'm living in much better."
The first episode opens six months after Jack the Ripper claimed the last of his six victims, The Ripper doesn't make an appearance in Ripper Street as the officers of Division H are forced to reflect on their inability to bring the infamously elusive murderer to justice.
"I've never been particularly fascinated by Jack the Ripper," says Rothenberg, who believes that his grim crimes have since been eclipsed by the even more gruesome and prolific deeds of those who have followed in his awful footsteps. "He was just the first of the serial killers and by today's standards, he's probably quite tame as I grew up on Jeffrey Dahmer and John Wayne Gacy.
"Jack the Ripper is more of a mystery, which is what makes him so powerful because no one to this day knows who he was. As horrible as what he did was, we've all heard so much worse; we've seen the pictures and we've heard the interviews."
Ripper Street screens on UKTV Mondays at 8.30pm.