Regarding the earlier conviction of Maggs, some snippets from an article in The Times (1 Nov 1852)
"At the Somersetshire Sessions this week, William Maggs, a notorious burglar, the head of a gang which has long infested the neighbourhood of Frome, was found guilty of stealing a quantity of milk, and sentenced to 15 years' transportation."
"A man named Wheeler swore positively to having seen the prisoner Maggs and one of his companions (Sparrow) milking farmer Allard's cows on the 6th of June, that he went up to them ... but they threatened to beat his brains out with a large bludgeon."
"He violently resisted being captured, and it was not until a strong body of constables arrived, and threatened to shoot him if he resisted, that he surrendered."
"The jury immediately found Maggs guilty, and he was sentenced to 15 years' transportation. There is also a charge of burglary for which he will be tried at the next assizes." [The other charge resulted in transportation for life.]
Reading between the lines ... Maggs, Sparrow and Hurd were evidently well known for their criminal activities in the local neighbourhood and Maggs, at least, appears to have had a violent temperament. It may well be that the local community "knew" that they were responsible for the rape and murder of Sarah Watts, but that the evidence was so flimsy that the jury had no alternative but to find them not guilty after only 20 minutes deliberation.
I doubt whether the jury were fearful of reprisals given that Maggs, Sparrow and Hurd would have been hanged if found guilty. (Unless of course there were other members of the gang ...)