McGuane went on to tell the AP that Montana has "one of the highest suicide rates in the nation" and urges those with mental illness to seek help.
"It's a very unique sort of grief and pain", McGuane said.
Kidder is seen with Prime Minister Pierre Trudeau as she arrives at the premiere showing of the film Louisiana in August 1984 in Montreal.
The death of Margot Kidder, an actor best known for her role in Superman, has been ruled a suicide. Additional high-profile roles included her part in 1979's The Amityville Horror and 1975's The Great Waldo Pepper, opposite Robert Redford. Kidder also appeared on the Smallville TV series, and she most recently appeared on The Neighborhood as Maggie.
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Kidder was diagnosed with bipolar disorder and eventually suffered a public nervous breakdown in 1996 after facing several career setbacks in the early 1990s, including a vehicle crash which resulted in her being paralyzed for two years.
Kidder, originally from Yellowknife, Canada, was a political activist who was arrested in 2011 in a Washington DC protest over the proposed Keystone XL pipeline from Canada's oil sands.
Kidder was found unresponsive at her home in Livingston on May 13. Kidder later said she suffered a manic episode.
If you or someone you know is dealing with suicidal thoughts, you can call the National Suicide Prevention Lifeline at: 1-800-273-8255.