33-year-old Landaeta was the father of Castro's 1-year-old daughter, but their relationship was far from healthy--Not when they were dating, and not afterward.
In fact, Castro had recently gotten a restraining order against Landaeta for issues of domestic abuse. She had no obligation to see him anymore, but she chose to maintain some contact.
To say that Castro's family disapproved of Landaeta would be an understatement.
"When she got pregnant by him, my heart dropped," Karina's father, Martin Castro said while firefighters cleaned the blood from the site of Castro's death.
According to Danielle Gannon, Karina's grandmother, Landaeta was a well-known paranoid schizophrenic. He was medicated, but he often used his condition as an excuse for violent and degenerate behavior.
He also drank heavily, a habit that no person taking schizophrenic medication should indulge in.
The night before the murder, Castro and Landaeta had engaged in an explicit argument over Snapchat.
"F*** around and find out," Landaeta warned the 27-year-old. "U wanna put a target on my back, u homies gonna know the real u."
Castro, described by her grandmother as a strong and stubborn woman, told her ex, "Dude, go head try and take my a** out."
The dispute clearly escalated into the next day, when Castro came outside of her apartment to meet Landaeta, first making sure that her daughters were safely inside.
After the beheading, Landaeta was taken into San Mateo County Jail with no bail, where he will await trial for the homicide of Karina Castro.