I am by no means an expert on this, so take this snippet of free advice for what it's worth.
First, the suggestion of making your own sterile saline solution is an excellent one. You need something to irrigate the wound. A further suggestion on that score would be to sterilize (boil for a few minutes in water) whatever container you intend to use. A dish soap bottle will work just fine for this purpose.
Neosporin is also a very good move. The easiest way to apply the topical cream is with cotton tipped swabs. This is of course, after you have fully and thoroughly irrigated the wound site. You'll want to flush out as much of the wound as you can.
I'd suggest using every bit of that quart recipe on this wound. There's no such thing as getting it too clean. You can dry the whole area with sterile gauze pads (available at any pharmacy or drug store) after you've flushed the wound with the saline solution.
Once the wound is dry and clean, apply the Neosporin generously. Try to keep from applying this to the surrounding area as it will prevent a successful completion of the next step.
Finally, once you have the wound clean and treated with the Neosporin, cover this whole bit of nastiness with a sterile gauze pad and bandage tape. You can aquire both at the same time you purchase the sterile gauze pads. Tape the gauze pad down just around the edges of the pad. You don't need to wrap the entire bird.
If you cannot obtain the bandage tape, use a series of regular band-aide strips to secure the gauze pad.
If it were me, I'd keep the roo isolated until such time as the wound has closed up or scabbed over. This will help prevent the other birds in your flock from pecking at it and thus further stressing your roo. He has enough on his plate right now without becoming "hen pecked"
If you've already lost one bird to this predator and have wounds on a second, you might really want to put together a good first aid kit for yourself. Better to have it and not need it, than to need it and not have it. And let's face it, accidents and injuries don't always wait for convenient hours to happen.
I think I'd be looking around real hard for what caused this whole incident, because that wound absolutely looks like some kind of predatory attack to me! Have you any ideas?
