The Business Development Manager position fits into Sales or Marketing Department? who does he report to?

YES  ,,,,    THEY ARE MUCH INTER LINKED TO EACH OTHER SO B. D , MARKETING & SALES HAS TO BE IN ONE DEPARTMENT TO SHARE & LEARN FROM EACH OTHER,,,,,,,,,,,,

That's a good question for which I never could find a suitable answer. There is a heavy discussion about where does the business development fit? Is it marketing or sales.  

Business development includes tasks that belong to Marketing such as brand placement, market expansion, new user acquisition, and awareness.

But it also includes sales activities, such as qualification and negotiation. 

I think it is more a sales-like job as it is mostly creating business through strategic relations including partners and corporate accounts. 

I think BD could be either part of Marketing Dept or Sales, whenever there exists not a BD dept in the company.

Marketing team considers them as their part, Sales Team as their own. Definitely, it is a part of both and difficult to segregate.  Many functions overtake these two departments as also the decisions. Let it be a management role representing both the departments with necessary intermediary functions between the two.