1) Like some mysteries 2) Not solved 3) Remaining a mystery 4) Unresolved 1) Mysterious 2) Strange 3) Unresolved 4) Unsettled 
The word unsolved means that any solution is not yet known; `many crimes remain unsolved;` `many problems remain unresolved.` In modern science there is still many open questions in many fields: Unsolved may also refer to: ...
[adj] - not solved
adjective not solved; `many crimes remain unsolved`; `many problems remain unresolved`