Marquez allegedly brandished a "BB-type" gun causing an officer to open fire, police said.
Officers spoke with her for more than 90 minutes, during the course of which she was uncooperative and they realized she was possibly suffering from mental health issues, the sheriff's department reports.
Police and a county mental health clinician had responded to the apartment complex where the actress lived to check on a resident believed to be suffering from a medical condition, according to the Los Angeles County Sheriff's Department.
Her acting career seemed to have slowed in recent decades, but she made waves in the fall when she accused George Clooney of blacklisting her after she had spoken up about alleged harassment on the set of ER. Marquez said, "women who won't play the game lose their career, I did".
Back in 2014, she wrote in an online post that she had spent her life savings on doctors.
"I had no idea Vanessa was blacklisted", Clooney said in a statement to TheWrap back in October.
Authorities confirmed her death on August 31, saying that officers went to Marquez's home in the 1100 block of Fremont Ave. after a landlord asked police to conduct a welfare check, Variety magazine reported.
Authorities said that officers had been called to the scene by Marquez's landlord who said that the actress was in "some kind of trouble". "I take her at her word", the actor said at the time. He was neither an actor, a producer, a director, or a casting director, he was "only an actor". At the time of her death, Marquez's Twitter account has been suspended. "The fact that I couldn't affect her career is only surpassed by the fact that I wouldn't".
Marquez had been vocal on social media about her struggles with various health problems, including what she described as terminal celiac disease, pulmonary embolism, osteoporosis and seizures.
The Daily Mail reported that Marquez was a long-time member of TCM Party - a group of "cinephiles passionate about classic movies". She has battled depression and obsessive-compulsive disorder, and appeared on a 2005 episode of A&E's "Intervention".