The plug- in was put in place but facility for normal users was removed by admins. I haven't tried to confirm why but I know that many people liked to share the info and there were many complaints about it.
If they want you to know their previous names they can as well post it on their profile. Or stick to a name they like and can live with.
You can contact a mod and ask the old name if you believe they murdered someone and trying to hide under new alias or something like that.. :| ( provide evidence please

)