If the investigation of the wife's murder overtakes that of Banks, especially to the detriment of the Banks investigation, then, yes, it would be the inciting incident.

But, curious here - is he a police detective? In Australia, this would bring 2 issues. After the death of a loved one, a detective would not be allowed to investigate a case until official grief counselling had taken place, and if he was already on a case - such as this - he would be removed. And second, as his wife had a connection with Banks, he would never have been put on the case in the first place.

As a Private Investigator, none of that would matter, except he would be completely messed up after his wife's death, and that would really affect his ability to think clearly.

Sorry to be a damp squib.