Word that means "spoken so as to make clear there is no arguing"
Contend has a meaning of to assert or maintain earnestly . Also, although it doesn't start with C the word asserted would be suitable as well.
After reading your question again, although there are a few words that come to mind, such as conclude (as already suggested by Nihal) and convince (which incidentally enough has an etymological relation to vanquish), the only one that makes much sense to me in your provided context is the word Confirm, with the following definitions from An American Dictionary of the English Language (A.D.E.L.) by Noah Webster:
- To make firm or certain; to give new assurance of truth or certainty; to put past doubt.
The testimony of Christ was confirmed in you. 1 Corinthians 1:8.
Putting a claim past doubt seems to match the described concept. However in your provided context this definition is not the one that actually makes much sense. I'd rather think that this meaning makes more sense:
- To make more firm; to strengthen; as, to confirm an opinion, a purpose or resolution. — A.D.E.L.
And one of the ways this is often done is by reiterating what was already said, especially if you are verifying the words of another person. Hence the following definition of the word Confirm excerpted from Wiktionary:
- To assure the accuracy of previous statements.
Which probably uses the following definition of the word Assure, which is also excerpted from Wiktionary:
- (transitive, followed by that or of) To give (someone) confidence in the trustworthiness of (something). [All Wiktionary text is licensed under CC-BY-SA 3.0 terms]
It makes quite a fair amount of sense in the context of being questioned by the police, who often make inquiries to the the truth behind allegations, and need evidence such as the verification of witnesses to do so effectively.
Compare your provided context:
"We were playing pool all night," Tom [confirmed] to Dick when Officer Harry questioned them as to where they were at the time they murdered that one guy.
To these quotations:
Before she got into the car she said, "Officer, please, he didn't do anything. I blocked his car in so I can get him in trouble. Please, Officer, don't take him to jail. He's the only person I got that will take care of my girl. Please, Officer, everything, it was me. Ask her. Tashelle, tell him y'all was trying to leave, and I pulled my car in to block y'all from leaving." I confirmed to the officer that what she was saying was true, but I didn't think it would make a difference. But the female officer was quite understanding; she uncuffed Tony and told him that he was lucky. — From Behind This Chair by Sarahca Peterson, p. 86 ©2010
Shortly after Mrs. Snake's funeral, I received a call from a police officer. I was in the kitchen when the call came and I knew to sit down. When I confirmed to the officer that Ryan was my brother, he explained that Ryan had passed. He had taken his own life, hanging himself in a homeless shelter two days after his birthday; he died a mere fourty-five minutes from where I attended school.
My Fields of Everything by Angelika Crescenzi ©2014
Granted, Dick is not an officer in your context, but the common theme here is the verification of another party's express or implicit report. In your case, I suppose Dick heard the allegations from the police officer and requested confirmation from Tom. Also, as long as I have mentioned it, I may as well give some of A.D.E.L's. definitions of Confirmation:
4. The act of giving new evidence; as the confirmation of opinion or report.
5. That which confirms; that which gives new strength or assurance; additional evidence; proof; convincing testimony; as, this fact or this argument is a confirmation of what was before alleged.
Part of my apprehension to these other options I considered earlier, given this sentence, is twofold: One is that it is not entirely clear to me that the other options quite so often mean to actually say anything, and the other is that it would be odd to follow them with the word To [somebody]. Google nGrams suggests that concluded to him and convinced to him simply never occur in written English, whereas confirmed to him does show at least some results, despite a drastically decreasing frequency in overall usage:
However, this doubt is predicated on the assumption that your given context accurately reflects what is wanted, which is not certain to me since you are trying to recollect another person's words, and there are cases where concluded to would be used so I have not entirely ruled it out as an option. However, that is a suggestion for another answer to make. This one suggests Confirm.