How the iPhone locked itself?

I work at a metro pcs and a few days ago a guy came in and he got an iPhone case. When i was about to check him out he realized he forgot his wallet. He handed me "his phone" and said i can hold on to it as insurance that he will be back to pay for the case and he took off and never came back so yesterday i opened the phone as it had no lock to look for a number to call but it was clean except a few pictures which did not looked like the guy who gave me the phone. I saw email notifications so i opened the email app and an error came up saying first connect to the internet. So i connected to the Wi-Fi and soon after the phone got locked and text pooped up saying " i possess a unique set of skills, i will find you and i will kill you " any idea how the phone got locked when it didn't even had lock before? And why that text pooped up?

Yes. The phone was stolen/ found & kept and the real owner has activated the iPhone feature found within the Find My iPhone app. It likely activated when you connected to the internet. Most people add their phone number to the message so that you can call them and arrange return.

The phone can only be unlocked now by the owner in a two-step verification process. If the phone is taken to any store to be unlocked they will call the cops unless you can prove your identity.

Drop it off at your local police station and be done with it.

It was a scam, the phone wasn't his and the real owner locked it remotely. The owner can also put a remote message on the screen that you can never remote, its a feature iphones have built in.

Oh no you connected to the Internet and he has information also it might have fallen asleep or he has hacked into it and has change it