Actors Jared Leto and Rami Malek sometimes find it difficult to shake off playing darker characters on screen.

Both Oscar-winners star alongside two-time Academy Award winner Denzel Washington in the crime thriller "The Little Things" about the hunt for a serial killer in Los Angeles.

Leto, 49, told Fox News, "Usually, at the end of a film, I put in the necessary amount of time and energy and I'm ready to leave it be, but if you're visiting some darker territory, if you're on a set that's maybe emotionally a bit darker, it can grab a hold of you and be difficult."

The actor-musician plays Albert Sparma who is the prime suspect in the haunting murder mystery. 

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(L -R) Rami Malek, Jared Leto, and Denzel Washington in a scene from 'The Little Things.'

(L -R) Rami Malek, Jared Leto, and Denzel Washington in a scene from 'The Little Things.' (Nicola Goode/Warner Bros Pictures)

Malek, who plays Detective Jim Baxter, echoed his co-star. "Every night you're going into that script and that story and looking at crime scene footage or pictures. That stuff is definitely going to affect your subconscious," he told Fox News. 

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"I think with the amount of preparation that we put into this, there's a layer that's very subversive and getting into your subconscious to the point where you might even have dreams about it," Malek, 39, admitted. 

Meanwhile, Washington, 66, prepped for playing a homicide detective by watching the TV series "The First 48."

Denzel Washington says he watched true crime 'The First 48' to prep for his role. 

Denzel Washington says he watched true crime 'The First 48' to prep for his role.  (Warner Bros. Pictures)

"I watched them all, behavior, getting used to looking at death and how [detectives] dealt with it," he explained to Fox News. "I must have watched every episode of 'The First 48.'"

Washington is no stranger to playing law enforcement characters.

"I have the utmost respect for what they do, for what our soldiers do, [people] that sacrifice their lives," he told Yahoo Entertainment. "I just don’t care for people who put those kind of people down. If it weren’t for them, we would not have the freedom to complain about what they do."

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"The Little Things" premieres Jan. 29 in theaters and on HBO Max

Fox News' Liza Aristizabal contributed to this report.