Deleting locked files

Select the item in your Trash, and choose Put Back from the secondary menu. Click once on that item, and press command+i. On this Get Info panel, you will see a locked category that is checked. Uncheck that, close the Get Info panel, and again, move that item to the Trash. Empty the Trash.

have we tried enabling permissions on the file?

there is a box that pops up when you type cmd-i and in the lower area has users permissions, try unlocking that, or switch users.