A man sent to Texas' death row for killing a Richardson police officer in 2018 could have his sentence overturned.

Brandon McCall's court-appointed attorneys are attempting to convince a Collin County judge that the convicted cop killer had bad legal representation during his capital murder trial.

McCall returned to the Collin County Jail from Texas death row where he's been living for the past 5 years. He was convicted in 2020 of killing Richardson Police Officer David Sherrard inside an apartment.

Body cam video obtained exclusively by CBS News Texas captured the moment Sherrard led the charge inside the unit after another officer broke down the door.

That's where McCall had fatally wounded his roommate and was lying in wait in a back room with an AR-15 rifle when the 37-year-old officer approached and was shot in the neck.

Now, McCall's court-appointed attorneys along with a forensic psychologist argue that the 33-year-old convicted killer deserves a new sentencing trial.

"They called him evil, cold-blooded," said McCall's appellate attorney. "In reality that was anything but the truth."

McCall's attorneys argued during opening statements that the defense team during the murder trial did not bring up evidence of their client's troubled childhood which included abuse and mental health issues.

But Collin County District Attorney Greg Willis is opposed to resentencing and contends that McCall got a fair trial.

"Brandon McCall got a very effective defense, but what I would like to say is, 'Go back to the trial. Think about what the jury saw,'" said Willis. "I mean, first of all, the body cam footage was graphic. It was horrific, and it was undeniable."

The forensic psychologist who testified Monday refused to answer questions from CBS News Texas, but on the stand, Jolie Brams criticized McCall's trial attorneys for not allowing her to tell the jury about chronically miserable conditions she said he grew up in that might have warranted a life sentence in the case.

Under cross-examination by Collin County First Assistant District Attorney Bill Wirskye, Brams was confronted with emails she sent after the trial saying "...the defense did a good job."

She was also questioned whether she was just bitter about being left out of the trial by the defense, admitting under cross-examination, "I was disappointed I didn't get to testify."

Sherrard's widow was in the courtroom Monday supporting prosecutors who believe the judge will not overturn the sentence.

McCall sat quietly inside the courtroom during the hearing which is expected to last for a few days before Judge John Roach decides whether to grant the request for a new sentencing trial or send the convicted killer back to death row.