What was Gonzalo's part in the overthrow of Prospero?

In Act I Sc.2 Prospero narrates to his daughter Miranda how his wicked brother Antonio usurped his dukedom. Miranda interrupts her father's account by asking him why her uncle Antonio did not kill them both straightaway,

"Wherefore did they not
That hour destroy us?"

Immediately, Prospero replies that Antonio and his accomplices feared public opinion because all the people of Milan loved and respected him and would not have tolerated their being murdered by Antonio. Instead they pretended to exile Prospero and Miranda to a distant land and put them on board a ship; but midway on the high seas they transferred them both onto a leaky boat and set them adrift hoping that they would soon drown:

"Dear, they durst not,
So dear the love my people bore me, nor set
A mark so bloody on the business, but
With colours fairer painted their foul ends.
In few, they hurried us aboard a bark,
Bore us some leagues to sea; where they prepared
A rotten carcass of a boat, not rigg'd,
Nor tackle, sail, nor mast; the very rats
Instinctively had quit it: there they hoist us,
To cry to the sea that roar'd to us, to sigh
To the winds whose pity, sighing back again,
Did us but loving wrong."

The treacherous Antonio had assigned the task of eliminating both Prospero  and Miranda to the nobleman Gonzalo. It was Gonzalo's job to ensure that the people of Milan were led to believe that Prospero and his daughter Miranda were accidentally drowned on the high seas. But Gonzalo being a benevolent man provided them both with all the necessary means and  provisions for their survival. Not only that, he even smuggled out some of Prospero's books from his library so that Prospero could continue his research and studies in another country:

"Some food we had and some fresh water that
A noble Neapolitan, Gonzalo,
Out of his charity, being then appointed
Master of this design, did give us, with
Rich garments, linens, stuffs and necessaries,
Which since have steaded much; so, of his gentleness,
Knowing I loved my books, he furnish'd me
From mine own library with volumes that
I prize above my dukedom."