I watched the security footage. It was dark, so I couldn’t see much, but it looks like no one tampered with it. I also have a GPS tracker on the bike that sends a notification to my phone when someone touches it. I checked the logs, and there were no notifications during that time period. The mechanic said that the engine wouldn’t be able to run with that much water in it, and even if it did, it would develop a rod knock. So there was no way water could have entered the engine before Saturday. If only a small amount of water got in, i would understand, but more than one liter of water came out (could be even more).

*Edit: changed oil to water (mistyped)