“News came to him” means that he received a revelation through the Angel Gabriel. The following verses from the Quran were revealed:
9.107 And there are those who put up a mosque by way of mischief and infidelity - to disunite the Believers - and in preparation for one who warred against Allah and His Messenger aforetime. They will indeed swear that their intention is nothing but good; But Allah doth declare that they are certainly liars.
9.108 Never stand thou forth therein. There is a mosque whose foundation was laid from the first day on piety; it is more worthy of the standing forth (for prayer) therein. In it are men who love to be purified; and Allah loveth those who make themselves pure.
Muhammad is obviously the only person who heard Gabriel saying that the people of the mosque had bad intentions. For his followers this is enough proof. For honest legal proceedings allowing the accused to defend themselves, there should be more that this. Especially for the founder of a religion that claims to bring “justice”.
What is interesting is that the Quran claims in 9.107 that the people built a mosque as a preparation to fight Muhammad. This is indeed very strange. It is like claiming that the Saudis built a church in Rome in order to attack the Vatican. And then they ask the Pope to inaugurate this church. And the Pope has the Church burnt down while people are inside and claims Jesus had appeared to him in a dream and told him to do because the Saudis have bad intentions. Few people will believe the Pope.