Lt Mendoza said Marquez, who played nurse Wendy Goldman on ER from 1994-1997, appeared to be "gravely disabled" when officers first made contact with her.
Marquez had spoken on social media about her mental health struggles and her Twitter says she had terminal celiac disease.
Last year, Marquez made headlines when she accused ER co-star George Clooney of having her black-listed in Hollywood for speaking out about alleged harassment on the set of the medical drama.
Clooney was forced to release a statement denying he had any involvement in Marquez's waning career.
"I had nothing to do with casting," he said. "I was an actor and only an actor. If she was told I was involved in any decision about her career then she was lied to. The fact that I couldn't affect her career is only surpassed by the fact that I wouldn't."
Marquez had also starred in episodes of Melrose Place and Seinfeld.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.