Misty Upham
Juliette Lewis expressed her fears that her co-star Misty Upham may have been murdered. Facebook

Actress Juliette Lewis has revealed that her friend and co-star Misty Upham 'feared she could be murdered'.

Upham, 32, was missing for 12 days before her body was found at the bottom of a wooded embankment in Auburn, Washington.

Police investigating the circumstances of the actress's death have claimed there is "no evidence of foul play."

The reports have outraged Lewis, Upham's August: Osage County co-star, who reacted to the police claims by demanding an urgent investigation.

Writing on Twitter she said: "#RIPMistyUpham I am in shock and greif [sic]. I pray the police do a murder investigation. They're saying not "foul play" when ofcourse it is."

She voiced Upham's own fears that she might be murdered for speaking out about brutality she suffered as a native American Indian, from her own community. The actress was a member of the Blackfoot tribe.

Lewis wrote: "I cant sleep. Too much darkness. I feel so sad about Misty. I know she has more to say. And about how she died.

"Misty told me about horrible violence she suffered on NA reservations She felt she coul be murdered! Bcuz she was vocal #ThisIsNOTaSUICIDE."

"Misty spoke out alot against injustices within Native community. And had known enemies. Police must do an investigation."'

She then retweeted a series of Upham's own tweets, including a warning for people to 'walk on egg shells' because she had 'just been followed by Indian Trader'.

"Misty Upham survived many things that many don't early on in life. She fought for the voiceless feircely [sic]. She understood suffering and the deepest pain. She had a presence everyone saw and felt. It is this presence that will continue," Lewis wrote.

"Out of the dark space in which her light got dimmed. I will remember her as tuff [sic]. Wise. Funny. Spiritual. And hopeful.

"This is another great reminder to call and check on someone when you think to. Not when its too late. RIPMistyUpham."

The Native American actress won praise for her roles in movies including August: Osage County, Frozen River and Django Unchained.

She was reportedly taking medication for anxiety and bipolar disorder. The actress was also believed to be struggling financially and had trouble paying her rent.

Her father, who identified her body, refuted suggestions that she was suicidal.

"It wasn't like she just decided to take time off," he said. "She has said suicidal things in the past but never followed through,' he said. "She doesn't believe in killing herself. She believes that is a sin and she would never do that."

It was reported that the police have responded to suicide calls at her residence on previous occasions. People magazine reported that in the last year, police were called to Upham's apartment four times following suicide calls.

Police received a suicide call on October 5, but when officers arrived, she was no longer at her father's house. A day later, her father asked that her daughter be listed as a 'missing and endangered person,' however the police said that Upham's case did not meet the criteria because her disappearance was not 'unexplainable, involuntary or suspicious.'

Speaking to HollywoodLife.com, Mona Upham, Misty's mother, accused the Seattle area police of not doing enough to find her daughter, attributing their lack of concern fir the case to her Native-American background.

"I think if Misty was different-looking they would be doing a lot more to help find her," she said.

Upham had recently returned to the Seattle-area to help care for her father, Charles Upham, who suffered a stroke last year.

The cause of her death is still unknown.