Countess Helen Mattoni, aka Louise Rogers (Rosemary Harris) is the main villainess from "I Killed the Count," a three part episode from the second season of Alfred Hitchcock Presents.
Countess Mattoni appeared in Part 2 under the name Louise Rogers, and she was inquired by Inspector Davidson regarding the murder of Count Victor Mattoni. Louise stated that she had no info regarding the case, but in Part 3, Louise was shown passed out inside the home, while she was revealed as Mattoni's wife, as well as the daughter of Lord Sorrington--one of three men who confessed to murdering the count.
After coming to, Helen revealed to Davidson that she had killed her husband. She got into an argument with the Count, which included the Helen stating to Victor that she could kill herself. Victor gave Helen a handgun, only for the Countess to decide to kill Victor instead. After a struggle with the gun, the evil Helen shot and killed Victor, and during her confession, she showed the scratch marks that proved her case. Sorrington and his friends Bernard K. Froy and Pat Lummock (aka Mullet) had secretly colluded to kill the Count and set up the evidence accordingly, knowing that a loophole would prevent them from being charged and convicted of the murder became only one of them could have done it. However, Helen actually killed the Count before they could get the chance, and she was thrown into the conspiracy, as the three of them continued to claim they committed the murder.
Hitchcock's summation revealed that Helen and the three conspirators were put to trial and were given light sentences, mainly due to the fact that the Count wasn't a pleasant person.