What is the difference between 怀疑 and 疑惑?
怀疑 is a verb for 'to suspect'


Example: 我怀疑他杀了他儿子 (I suspect he killed his son)


  怀疑 is also a noun for suspicion (2.the state of mind or feeling of one who suspects)


Example: 这只是我的怀疑 (It is only my suspicion)


  疑惑 is an adjective for 'uncertain (2. not confident, assured, or free from hesitancy); puzzled'


Example: 你这话使我感到疑惑 (these words of yours make me feel uncertain) 


  疑惑 is also a noun for ' doubt; uncertainty; puzzle'


Example: 有疑惑 (have doubt) ; 重重疑惑 (layers upon layers of uncertainty); 这个疑惑 (this puzzle)


  嫌疑 is noun for 'suspicion' (4.state of being suspected)


Example:他有杀了他儿子的嫌疑 (he is under the suspicion of killed his son)