Tesla CEO Elon Musk has acquired a 9% stake in Twitter to become its largest shareholder while joining other critics in questioning the social media platform’s dedication to free speech and the First Amendment.

Musk’s ultimate aim in acquiring 73.5 million shares, worth about $3 billion, isn’t clear. Yet in late March Musk, who has 80 million Twitter followers and is active on the site, questioned free speech on Twitter and whether the platform is undermining democracy.

In years past, Twitter and other social platforms have taken fire for allowing harmful speech ranging from incitement to violence to coordinated harassment and racial abuse. More recently, these platforms have made concerted efforts to rein in such behavior, often drawing criticism similar to Musk’s from the political right. Both Twitter and Facebook faced blowback after suspending the accounts run by former President Donald Trump following the Jan. 6 Capitol insurrection last year.

It’s unclear just when Musk bought the stake. A U.S. Securities and Exchange Commission filing made public on Monday says the event triggering the filing happened on March 14. Musk has also raised the possibility with his massive and loyal Twitter following, that he could create a rival social media network.