There are two things wrong with the statement. Galileo was not killed; he died of natural causes while under house arrest, nine years after his trial. The other is that the roundness of the planet was never in question - even in the Middle Ages, centuries before Galileo, it was taken as fact, even in church sermons, that the Earth was round. He was put on trial for claiming that the Earth revolved around the Sun, being an obnoxious little shit about it, and not having the evidence with which to back it up.

There's a whole bunch of posts already dealing with these, so let's take them by subject. First, on the matter of planetary shape, u/jschooltiger examines the matter here, and also in the context of timezones; also u/qed1 in this post, and u/sunagainstgold on just how accepted references to a round Earth was.

For Galileo himself, see next post.