The only regret that Joan Faye Hartman showed the night her son’s girlfriend was stabbed in the heart at their Slidell home was when she considered the possibility that she hadn’t finished the job.

Hartman’s riveting account of 27-year-old Tanya Knower’s stabbing death in 2012 was played on video before a jury Thursday in Judge Scott Gardner’s St. Tammany Parish courtroom, where the 56-year-old grandmother is on trial for second-degree murder.

The prosecution, led by Assistant District Attorneys Jason Cuccia and Nick Noriea Jr., presented the state’s case Thursday, calling witnesses who had gathered evidence at the house where Hartman and her husband lived with their son, Richard Hartman, Knower and their 6- and 9-year-old granddaughters.

The video showed that moments after St. Tammany Parish Sheriff’s Office Detective Randy Loumiet read Hartman her rights in an interrogation room, the defendant asked how Knower was doing. Loumiet didn’t tell her that the mother of her two granddaughters was already dead.

Hartman cut straight to the point. “I wanted her dead. I didn’t do that to see her hurt; I wanted her dead. I still do,” she said matter-of-factly.

Minutes later, she grumbled that Knower was going to be fine. “That bitch is going get better like she always does,” she said.

The white-haired Hartman, dressed in pale pink pants and a white sweater, was pale and quiet in the courtroom, stoic as her interrogation played out before the jury. Only when she returned to the defense table did she show emotion, dabbing at her eyes with a tissue.

But on the courtroom television, Hartman was defiant and angry, pouring out a bitter flood of grievances against Knower, who she said was a pill addict who neglected her daughters, one of whom is autistic, leaving Hartman to handle all their therapy appointments and school responsibilities.

She called Knower names like “pig” and “bitch” and recounted previous physical altercations, including an incident where the younger woman stabbed her.

“She stabbed me first. She stabbed me years ago, and I never got an apology for that,” Hartman said. That happened eight years before, but Hartman said she reminded Knower about it when she plunged a knife into her back. “This is how it feels, bitch,” Hartman said on the videotape as she pounded the table in the interrogation room.

Defense attorney Martin Regan Jr. questioned Loumiet about the defendant’s actions that night, pointing out that Hartman had taken a two-hour walk after the women had argued earlier in the evening. Hartman had wanted her granddaughters to go to church the next morning, but their parents had plans to go to the zoo instead.

Regan asked if anyone else had taken steps to de-escalate the situation, and Loumiet said no.

The defense attorney also questioned Loumiet repeatedly about Hartman’s emotionally charged state and her deep concern for her granddaughters, including a letter that she asked the detective to give her son outlining what needed to be done to care for the girls.

Regan hammered on Hartman’s concern for her granddaughters’ safety, including a statement she made about fearing for their survival.

“Until she (Knower) is dead, those kids don’t have a chance in hell,” Hartman said at one point during her questioning by detectives.

Regan asked Loumiet if the law allows someone to act in defense of others.

“She’s almost a martyr, isn’t she?” the defense attorney asked.

“In your opinion, sir,” Loumiet replied.

Earlier in the day, forensic pathologist Michael DeFatta, of the St. Tammany Parish Coroner’s Office, testified that Knower had received two stab wounds. One entered her back, cutting through the backbone and piercing the aorta and the heart itself. The second wound, to the abdomen, punctured Knower’s intestines and stomach but likely was delivered during or immediately after her death, which would have occurred in minutes, the pathologist testified.

Hartman’s account backed that up. She recounted stabbing her son’s girlfriend first in the back with the intent to kill her, using a knife that Hartman said she had bought a month earlier for that purpose.

“She got it in the stomach because it pissed me off that she was still breathing,” Hartman said.

The fight between the women escalated upon her return from her walk when Knower told Hartman she had packed up all of the girls’ pictures and artwork they had made, including drawings they had made for Hartman, and said she was taking the girls away, the defendant recounted on the video.

After a break in the interrogation, Loumiet returned and handcuffed Hartman, quietly telling her that Knower was dead.

“Thank you, God,” Hartman said. She then told Loumiet several times that she was prepared to face the death penalty or life in prison. “I don’t need a lawyer and I don’t need a jury,” she said, telling Loumiet he did not know how much Knower deserved what happened.

“She put me through hell,” Hartman said. “If she was just a mother, she’d still be alive.”

Follow Sara Pagones on Twitter, @spagonesadvocat.