Um, how did he get the email address or phone number or whatever of your (former) colleagues?

He may be 'sick', but he is bothering people. Unwanted contact. Put stress on you, and others, wondering what he's going to do next - especially if it's getting worse. Whether he's penniless or not doesn't matter. His behaviour has to be stopped somehow.

Also, if he has many 'victims' already, he might not stop with you and those you know. He might go after other people as well.

I had to deal with someone who was harassing me at where I used to work, though not the same way.

You mentioned "corporate security". Was that your company, or the other company? If not yours, would that be a good idea to do the same?

The most important thing is to take care of yourself - keep safe.