Now, we are left wondering if he might kill again.
Last week, Leo punched Stephen after the latter dropped the bombshell that he had shared a kiss with Leo's fiancée Jenny Connor (Sally Ann Matthews). But even before he heard about this betrayal, Leo was already suspicious of Stephen's sneaky behaviour.
He set out to investigate and soon discovered that Stephen was planning to steal the equity from his mother Audrey Roberts's (Sue Nicholls) home in order to pay the money he owes to ex-wife Gabrielle (Helene Maksoud).
From the dangerous height of the factory gantry, Leo confronted Stephen, ready to call the police and Audrey to expose him. But Stephen couldn't let that happen and he fought against the younger man. This led to him pushing Leo away, who knocked his head and fell over the edge of the gantry.
Leo landed in the dustbin below, and a shocked Stephen rushed down to ground level - only to find he was already dead. The altercation clearly wasn't planned to end this way, but now Stephen was left with a huge mess to clear up. There is also the fact that Jenny, who believes she is moving to Canada with Leo later in the week, will soon notice that he is missing.
Stephen was forced to leave Leo where he was while his oblivious niece, Sarah Barlow (Tina O'Brien), insisted they headed out for dinner. By the time he was able to return, Stephen found unimpressed factory owner Carla Barlow (Alison King) with the police. This turned out to be because he had left the gantry door unlocked, and the police went on their way with no idea that a dead body was close by.
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Stephen then waited until nightfall before dragging Leo's body into an Underworld van to then dispose of him!
Speaking for the first time about Stephen's shocking act, actor Todd Boyce reveals whether he thinks his alter ego can cope with what he's done.
"It's really interesting, that. I'm not sure that he will, and I've thought about that," he says.
Discussing whether Stephen could kill again, he adds: "Someone was joking the other day, we were talking in the green room. Another actor's character had killed someone and he said, 'Once you do one, you kind of get a taste for it!'"
"I think it might get easier, so maybe he'll be able to cope with it," Boyce says of the possibility that Stephen could continue taking lives. However, he muses that he's portraying the story one step at a time as viewers prepare to see how the character is hardened by his actions.
"At this point, because I'm just taking this journey, I'm just going to play it like I would play it; see how toughened he gets."
Asked how he feels about taking on such a storyline, Boyce is thrilled as he hails Corrie's most famous serial killers.
"Connor McIntyre (who played Pat Phelan), I'm just so in awe of him; and Brian Capron [as] Richard Hillman. I'm just so honoured that Iain MacLeod [Corrie's Executive Producer] phoned me out of the blue and said, 'Hey, do you want to come in?'
"What an honour! I'm so honoured, basically! Someone believes in me enough to say, 'You can do that!' So I'm beside myself, I'm really excited about it."
The actor says that prior to his return following a 15-year absence from the soap, he was given an early idea of the path Stephen could take.
"Iain got me on Zoom and told me, with his amazing mind, and he just unleashed this outline. I was made aware I was going to be a murderer."
Viewers will have to wait and see what Stephen's next move will be as he aims to cover his tracks, but it certainly seems that the character is set to deliver more twists as time goes on.
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