There's no way to know it.
This was a company so for sure they bought it and put it in multisig accounts maybe even under custody of some insurance backed company like Bitgo.
You can't really know.
Is it hard to read a few posts and find out how MicroStrategy buys BTC - rather than continue to speculate and copy other people's answers? We know the way he buys, we know when he will buy approximately (there is always an announcement), but that doesn't help us at all because the way he buys never affects the price.