grammar

It depends on the context, for example:

"After much investigation, he came to the conclusion that the thieves had gained entry to the vault with the assistance of someone in the company."

"The company is pressuring me to come to a conclusion in the next 24 hrs., so, although my investigation is not complete, I'm going to tell them that it appears the thieves gained entry to the v

It depends on the context. Please post the whole sentence.

Anonymous which one is correct "come to a conclusion or come to the conclusion?"

Typically you "come to a conclusion" when you don't say what conclusion it is; you come to the conclusion that ... when you say what it is.

The committee has finally come to a conclusion on the matter of budgeting.
The committee has come