'Monsters' Actor Cooper Koch Says He Cares So Much For Erik Menendez

Cooper Koch's got a lot of love for the convicted murderer he played ... saying he cares for Erik Menendez -- and, meeting him in prison was a treat.

The actor -- who plays Erik in Ryan Murphy's "Monsters: The Lyle and Erik Menendez Story" -- spoke with Deadline at the Motion Picture Academy Gala Saturday night ... and, he says his meeting with Erik was "rewarding"

Cooper says preparing to play Erik was sort of like preparing to meet him as well ... explaining he developed a trust and care for Menendez over hours of preparation.

As you know, Erik slammed 'Monsters' as a dishonest portrayal of his and his brother Lyle's lives ... and, we told you the two received a visit soon after from Koch and Kim Kardashian.

Cooper said he actually got a hug from EM at the prison where the Menendez brothers are serving life sentences for murdering their parents 35 years ago. He later revealed he'd spoken to Erik who expressed his displeasure with the series before it came out -- so the criticism wasn't surprising to anyone involved.

Like many people -- including numerous members of the Menendez family -- Kim came out after the meeting and said the brothers deserve to be released from prison.

The Los Angeles D.A. is currently reviewing their case and deciding if his office will push for a retrial or a resentencing of the Menendezs that could see them released from prison.