Gary Scott Holland, 44, pleaded guilty on Nov. 8 to first-degree murder and agreed to the 50-year term.
Holland killed Horan, 46, on the night of Oct. 29, 2010, after he posed as a PG&E worker to get into the building in the 900 block of Chestnut Street, then knocked on her door.
Horan did not know Holland, who later told police he was upset about his wages being garnished for child support and had set out that night, high on methamphetamine, intending to rape someone.
Horan, who had just returned from a trip to Argentina with her mother Sharon, was killed with a pry bar and knife. Her body was found the next morning and Holland was arrested on Nov. 5, 2010, at Sutro Heights Park near Ocean Beach.
At today's sentencing hearing, Sharon Horan addressed the court to talk about her daughter's death.
"Optimism, joy and confidence are all beyond our grasp now," she said. "The loss is unbearable, but yet it must be borne."
Horan criticized a justice system that allowed Holland to be free. He had recently gotten out of prison after serving 11 years of a 13-year sentence for attempted murder in Fresno County.
"I cannot comprehend a ... system that allows a monster like this to live among us," she said.
Assistant District Attorney Michael Swart, who prosecuted the case, also read a statement by Elizabeth Horan, Kathleen's sister.
"Kate's life was taken by the worst kind of person and there was no reason for it," she said in the statement.
During the majority of the hearing, Holland sat with his head down. His defense attorney, Rebecca Young from the public defender's office, later read a statement to the court acknowledging the "tragic and senseless act."
Several people began weeping while Young read the statement, in which Holland said "not a day goes by that I don't regret" the killing.
"I will never forgive myself," he said.
Judge James Collins sentenced Holland to a 25-year term that was doubled to 50 years because of the prior conviction. He will not earn credit for good behavior so will not be eligible to parole until the end of the 50-year sentence.
As a part of the plea deal, other charges in the case were dropped including attempted rape, robbery and burglary.
Holland also agreed as part of the plea deal to waive his right to ever appeal the case, which Young said outside of court was a request of Horan's family.
"He wanted to end it for the family and for himself" and "give finality to the proceedings," Young said.
District Attorney George Gascon released a statement following today's sentencing.
"The sentence handed down today not only reflects the vicious and senseless murder of Ms. Horan, but ensures San Francisco residents that this violent predator will never walk our streets again," Gascon said.
"I hope that today's sentence allows family members and friends to begin the healing process."