Malcolm was in a custody battle with his ex-wife, Beatrice, over Matthias; meanwhile, Alicia wanted children of her own with Malcolm. Malcolm refused because he felt having Matthias was enough, and he was winning the battle due to his commitment. However, figuring that Beatrice would continue to fight for custody, and also harboring anger over not having kids of her own, Alicia plotted to kill her stepson. The villainess poisoned a water bottle with monkshood, which was growing outside the house, and later drove where Matthias was skateboarding to give him the bottle--which Matthias drank and later succumbed to the effects.
As part of her plan, the evil Alicia intended to make it appear that Beatrice and her church (which conducts exorcisms) killed Matthias, and she could finally have a child of her own with Malcolm. Alicia's reveal began with a nightmare from Jane Rizzoli, who envisioned Matthias laying dead before rising and giving her a purple flower. She later asked Maura Isles about the flower, which was later revealed as monkshood. The duo went to the Senna home and informed Malcolm and Alicia that Matthias was poisoned by monkshood, and it was there that Alicia was revealed as the killer. After denying it at first, Alicia confessed and stated that the continuous battle would be expensive and that she did it for Malcolm, who lunged at his evil wife in anger before being stopped by Maura and Barry Frost. Jane later handcuffed and arrested Alicia for her stepson's murder.
- Alicia Senna was Rizzoli & Isles' very first villainess.
- Laura Leigh Hughes also appeared on CSI: NY as the villainous Jennifer Stupaine.
- "You know she never would've stopped fighting for custody. We would've spent all our money on lawyers. It just was trapping us in the past, and I swear, Malcolm, I swear, I did it for us." (Alicia Senna revealing her motive for killing Matthias)