Well, from I know, the best you can do is create a filter (in the arrow next to the Reply button, click in "Filter" or something alike), so every new message from the spammer will go to that folder, and also deleted, if you choose.
Here and here you have some tutorials.
Block a Sender in Gmail 
To have Gmail send messages from a specific sender to the Trash
- Follow the Create a filter link (at the top of any Gmail mailbox, near the search buttons).
- Type the desired email address under From:.
- You can block an entire domain by entering just that. To block all mail from both firstname.lastname@example.org and email@example.com, type
- To block more than one address, separate them with "|" (the vertical bar; typically above the backslash on the keyboard; not including the
quotation marks). You can block both firstname.lastname@example.org and
email@example.com by typing "firstname.lastname@example.orgemail@example.com",
- Click Next Step ».
- Make sure Delete it is checked under Choose action.
- Click Create Filter.
- Check Also apply filter to __ conversations below to delete previously received messages.
To archive and label instead of delete messages, choose Skip the Inbox
(Archive it) and Apply the label: under Choose action when setting up