I think that at the time he was a sub Inspector it was said at the time of his Wife's death.
He must have been suspended as per Police rules and regulations and a proper Police Investigation must have been carried out by their specialist department because he was a Police Officer and surely they must have investigated properly for the case to be dismissed.
I don't him involved in any way at all in her death but I think that he may be sad that being a Police Officer he could not prevent her death hence him feeling guilty all the time.
I want Mini to find a Dairy or a Suicide note if She did take her life at all, but what I don't get is would she put her Mann through this pain if she truely loved him in the 1st place.
A clue might be her holding her head as the pain was unbearable to her, suggesting a long term illness being ignored by her Father to justify in putting the blame on HS instead of thinking of her taking her own life.