No one is able to delete a particular document from a document library

One of the very fresh incidents I have gone through. In my SharePoint farm for a specific documents library No one is able to delete a particular document from a document library

Below steps are followed to resolve this issue:
I tried using my Farm Admin account but no luck
I have tried to delete this doc using STSADM, Powershell, content & structure, and even SharePoint manager. All of which error saying the document is checked out or locked by a user. I have also tried turning off the Force check out feature.
No luck

The odd thing is, that the document icon, does not show as though it is checked out. And the drop down menu only has "check out", but when you try that, you get an error stating the document was NOT checked out.

If you try to delete via explorer view, it pops right back up after a page refresh.

When I look at its properties in SharePoint manager, it shows the document as checked out to that same user, but it also shows that I checked it in via content & structure. So it also says the checkout status is "short term", but I waited until the lock "should have" expired, and tried to delete it again. But no luck, it just pushed out the lock expiration.

This library has hundreds of documents; to delete it and re-create it would not really be a possibility. I am able to upload new docs and delete them.

Resolution
Finally none of the above steps helped me to delete the document so I used SharePoint designer.
Opened the site in SharePoint Designer and just browsed to that document library, selected those documents and deleted it, which was deleted without a question.

Still I am in search how this happened !!