@Keyta-Kun
Depending on the kind of "useless" you're refering to....
Muyou - useless, unnecessary, needless
Muri - useless, impossible, unreasonable
Dame - It's useless, Not a chance, No way
Only thing I can think of for the -tta part is he's saying it in a (casual) past-tense speaking style. If it were only casual past-tense, it'd probably be Dame datta. Speaking style in Japanese usually shortens words and drops a couple of characters, in this case the "da". So I guess in this case he's saying something like "No way (it could have happened)."