Police said the Eun Kang was four months pregnant with twins.
Washington faces three counts of murder with special circumstances. If convicted, he could receive the death penalty.
"He's facing three counts of capital murder and the special circumstances are that there were multiple murders," said L.A. County Deputy District Attorney Christi Frey. "There was an adult victim and two fetuses. She was pregnant with twins. Also, he's facing rape charges and sexual penetration charges."
Police allege Washington somehow got into the Kang's home, stabbed her several times and raped her. Kang's landlord called 911 at about 10 p.m., and when officers arrived, they noticed Washington running from the scene. Police believe Washington randomly targeted Kang.
Kang died at the hospital. It was discovered that she was pregnant with twins.
Kang's landlord, Arnold Springer, said he saw the whole thing.
"She was screaming, 'No! Don't do that, no!' I shined my light in there and I saw him," said Springer. "He was raping her. And I said, 'Don't do that! Don't do that! Stop that, I'm going to call the police!' and I banged on the glass window with my flashlight. And he didn't stop. He didn't even acknowledge that somebody was there. He just kept on doing it. I looked at my wife and we ran back into the house and called 911."
Thursday afternoon, Washington appeared in court, but his arraignment was continued. Authorities said Washington is on probation after pleading no-contest to burglary in September.
Court records show that case was delayed after Washington was declared mentally unfit. He spent several months at Patton State Hospital.
"Eun. Honest. Vibrant. Hard-working. Helpful. Conscientious. Decent. Wonderful young woman," said Springer describing Kang. Springer said the victim was a tenant of five years.
Kang was the owner of P-1 Cleaners on the lower level of a Beverly Hills office building.
Venice resident Jim Hubbard said he lives a block over, and stopped by the victim's home on Thursday to leave flowers.
"I have four children, four daughters. Any time, any time, particularly children are affected by the insanity of human beings, I'm outraged," Hubbard said.
Mary Jane Martin was walking her dog in the same area the night before the attack
"I remember thinking, it is so dark here. Why don't these owners, or the city, or somebody, I mean it's pitch black, you can't see anything, and the thought when through my mind. Someone could attack me right now, and nobody would be the wiser," she said.
Washington was being held without bail at the Van Nuys jail. He was expected to reappear at the Airport Branch Courthouse on December 17.
Anyone with information is urged to call the LAPD at (310) 482-6313.
The Associated Press contributed to this story.