Colin Madsen 'froze to death after taking cannabis', says law enforcement, but friends dispute findings.
Mother of 25 year old Colin Madsen flies to Russia as search is underway in Buryatia.
Colin Madsen, 25, enjoyed night-walking in Siberia but never came back after going out on Sunday.
Friends of missing American questioned using polygraph by police as search goes on for 25 year old student last seen early Sunday.
Forensic tests underway in America as mother appeals for Russian witnesses, alleging 'foul play' and police 'cover-up’.
Contradictory reports on cause of death as Colin Madsen's remains found in snow in mountainous region of Republic of Buryatia.
Law enforcement officers sought to 'force confessions from students' in case of US citizen Colin Madsen, found dead in Buryatia.
She accuses police of 'ineptitude', 'misinformation' and 'cover-up' over student Colin Madsen's death.