1. difficult to find the truth about sth
sth was shrouded in mystery
Something which is shrouded is covered or is obscured from view. Something 'shrouded in mystery' is very secret or mysterious or is something the general public do not know much about. "The religious organisation's activities were shrouded in mystery leading to many rumours." You could also use the expression 'veiled in mystery' or 'surrounded by mystery'.