Of course he has every right to say nothing and deny everything. But we have the right to call him a coward for doing so, and demand sterner punishment for someone who adds to the tragedy he already caused the family of the boy by his denying fairly obvious guilt.
I could be wrong, but I have read of more evidence that says the cop is guilty than I have that Osama bin Laden organized the September 11 hijackings, and I have no reasonable doubt about Osama.