The phrase "unclear circumstances" refers to a situation where the details or reasons behind something happening are not easily understood or known. Full definition
There are actually many cases in which insurance companies either contest the death of an individual under unclear circumstances as a suicide to avoid paying a large benefit. (secureseniorlifeinsurance.com)
In 1985, Andre married Ana Mendieta, a Cuban artist who died the same year, under still unclear circumstances. (widewalls.ch)
According to the Ministry, the two were inducted into the regional house of chiefs under unclear circumstances, hence nullifies their inclusion as members. (citifmonline.com)