The ex-jailbird who gave alleged Charleston mass murderer Dylann Roof a prison beatdown said his attack reminded him of the Alfred Hitchcock classic “Psycho.”

It was “like in the movies when the girl is in the shower and she gets startled,” Dwayne Stafford, 26, told the website Black Collective.

During the assault last week, Roof “didn’t speak whole sentences … it was more like whining … his cheeks were scarred,” according to Stafford.

The attack left Roof’s face and back bruised, according to a police report.

Roof and his attorneys did not press charges following the incident.

Roof has been in solitary confinement since he was arrested on June 18, 2015, a day after his deadly shooting rampage at Emanuel AME Church in Charleston.

Stafford was released from the Charleston County Detention Center on $100,000 bond a day after assaulting 22-year-old Roof — with whom he regularly spoke — on Aug. 8.

He said he wanted to wanted to cozy up to Roof — in order to get inside the sicko’s head.

“I wanted to approach him and see like what was you not getting for you to understand the fact that what you did is not understandable,” he said. “I approached him like, ‘What’s going on with you.’”

Stafford called the nine black worshipers whom Roof allegedly slaughtered inside a historic church last year “family.”

“Those nine people, that’s family because we live in the same state. We are one regardless,” Stafford said, adding that he was the first inmate to speak to Roof inside the prison.

Stafford said Roof was boasting to other inmates that he killed a 5-year-old, but Stafford corrected him.