Tsia-Lian Yu was driving in her car and then Ramirez decided to approach and stop her. While she was stopped, this psychopath goes up to Yu's car and pulls her out of it.
Joseph Duenas(the hero without a cape) runs out to his balcony after hearing Yu's scream for help. He ran inside and called the cops. When he ran outside he saw Ramirez get into her car and drive away. Yu was crawling on the ground and when the police found her she was unconscious but breathing. She had stopped breathing and they tried CPR until the ambulance showed up. But she was later pronounced dead at the Lake House Inn. Yu's autopsy showed she had been shot twice in the chest from short range. They recovered the bullet as evidence.
There was drugs being used a lot during this time. He used drugs so this could have some influence on why he was insane enough to do such ridiculous things.
The characteristics of someone who could commit a crime like this or any others that he had done would be: crazy, schizophrenic, evil, remorseless, merciless, cruel, and cold-hearted.
One probably did not have a very pleasing childhood(Like Ramirez who had a horrible childhood) and someone who probably lacked friendship and relationships.
He had been arrested at some point. He was found guilty of this crime as well as all the crimes he had committed. He was sentenced to the death penalty but he died in 2013 at the age of 53.