They believe 40-year-old Isaias Corona of Visalia shot and killed 26-year-old Kathryn Bradshaw, before turning the gun on himself.
Police were called to a home on Thompson and El Cajon just before 7 o'clock Monday morning.
Family members say the suspect is someone she had been dating for the past eight months.
The family of 26-year-old Katie Bradshaw consoled one another Monday -- after learning her boyfriend, 40-year-old Isaias Corona killed her, before turning the gun on himself.
It happened inside the master bathroom of a home in Visalia -- she shared with her brother.
"The brother had left. He came home at one o'clock in the morning and went to sleep," said Sgt. Gary Williams. "When he woke up this morning, he went to check on his sister when he located both of the individuals."
Investigators did not find any signs of a forced entry. They believe Katie's boyfriend came over with a shotgun sometime Sunday night. It was the same weapon friends tell officers they saw him with the day before.
"It's just tragic," said Sean Daily. "And we're all wondering what happened last night?"
Daily lives right next door and has known Katie and her family for years.
Katie's brother ran to him for help, after discovering the bodies.
"Watching someone's raw emotion, it's not easy," said Daily. "It's unlike anything I've experienced before, so it's very hard."
Daily says he didn't hear anything overnight. But one neighbor tells Action News -- her boyfriend heard people yelling from inside the home.
"He said he hear some screaming, the guy yelling, but he didn't think nothing of it," said Dolores Alvarez. "He just thought it was a couple fighting. It just tells you anything can happen no matter where you live at."
According to friends -- Katie worked with her dad, and graduated from Golden West High School in 2003.