Margot Robbie studied Jared Leto like a psychologist would to get to know him.

The 26-year-old star worked alongside the 44-year-old actor in hotly-anticipated movie 'Suicide Squad' and admitted she found it hard to ''get through to him at first'' because he was always in character.

She told Bustle: ''He's in character all the time. I spent a lot of time trying to figure out their relationship. Because he's got this facade up, it was really hard for me to get through to him at first. So I was like, okay, I gotta approach this as if I'm trying to crack the Joker.

''It's a test that psychologists use to determine what mental illness people might have. It's a list of 500 questions or something. Whenever we had time to rehearse or improvise, or even in scenes, I'd just start with those questions ... I'd see which ones would catch him off guard and how, how he'd react, and I'd be like, 'Okay, I'm gonna go for this tactic now.'''

Meanwhile, Margot previously revealed she accepted a role in 'Suicide Squad' without seeing the script.

She said: ''I never really thought to myself, 'Oh, I want to be in a comic-book movie'. When I first about it I was about to do a different project, and they said, 'Before you sign on for that, would you consider playing Harley Quinn?'

''I was like, 'Okay, can I read the script?' And they were like, 'There's no script.' 'Okay, is there anyone attached?' 'No one attached.' '... Is there a director?' 'Yeah, David Ayer.' And I was like, 'Well, I'm in!' And that was kind of it!

''I didn't sign on to do a comic-book movie, nor had I ever expected to. But if I was to do it, David was the guy I wanted to work with.''