General Synonyms:
* Doubtful
* Questionable
* Skeptical
* Wary
* Cautious
* Distrustful
* Uncertain
* Ambiguous
* Shady
* Fishy
* Odd
* Strange
* Eerie
* Uncanny
More Formal Synonyms:
* Dubious
* Specious
* Problematic
* Unreliable
* Untrustworthy
* Insidious
Informal Synonyms:
* Weird
* Off
* Funny
* Phony
* Sketchy
Synonyms related to specific contexts:
* Culpable: Implies guilt or responsibility for wrongdoing.
* Criminal: Suggests involvement in illegal activities.
* Incriminating: Provides evidence of guilt.
* Incriminatory: Tending to incriminate someone.
* Devious: Suggests cunning or deceitful behavior.
The best synonym to use will depend on the specific context of your writing.