thorough investigation

to investigate thoroughly

event, incident / matter, affair / scandal

To perform; to do; to conduct oneself; to carry out.

guess

examine

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend

distal demonstrative, something far off removed from both speaker and listener: that, yon / particularly, male personal third person pronoun: he / by extension from he: boyfriend

he; boyfriend

a difficult (to solve) case