Under the circumstances Mr.Grimshaw is afraid that Bart's story will make it difficult for Amos to prove his innocence.

Just think of it.

That boy was lost and wandering around in the woods at the time o' the murder.

As to that scar, Amos says that he ran into a stub when he was going through a thicket in the night." Uncle Peabody shook his head with a look of firmness.
Again Grimshaw laughed between his teeth as he looked at my uncle.

In his view every man had his price.
"I see that I'm the mouse an' you're the cat," he resumed, as that curious laugh rattled in his throat.