I can honestly say I knew cos Dexter always spoke about almost surgical precision, medical knowledge, neatness etc. Haha, im good at guessing, lol. Plus it was really convenient that he dealt with amputees, come on!

Haha I really had no idea until he said 'I studied the human form.'

Come on guys. xD

I knew the minute he became Debs boyfriend.

well this question spoiled the show for me after seing the pictere and it saying i knew onder it but watever i thought it was him when i seen him . He looked suspicious

FFS PUT UP A SPOILER ALERT!! Honestly this question ruined the first season for me, please consider this in the future

well i honestly thought at first that it was deb, i mean come on if dexter was a serial killer raised by Harry then maybe deb was too.

I knew because I read episode descriptions on IMDB. I wish I hadn't.

the rest is And th ice truck killer cuts up body parts

:)**** $^ ^$ ****
********* ( *******

I thought it was Angel at first.

The second time I saw Brian I figured it must be him. Although I totally didn't see the brother relationship thing coming!

all these damn serial killers were so charming i didn't even pay attention. lol jk. i kind of thought it was this guy even before they suspected him ->

but i had no idea it was brian until we saw him at his place with the doll.

I knew since the scene in the hospital, he looks a bit suspicious to me xD

Once I saw the nail polish and the hands I knew.

I had this crazy idea that Debra's boyfriend would make an excellent potential killer-victim for Dexter(if the writers wanted to go to that direction, which as it turns out they did), but i didn't connect him with the ice-truck killer till we saw him in his apartment with the doll writing the Barbie message to Dexter.

And when he said "I studied the human form", i got a total Hannibal-Lecter vibe.

I knew, but the big bro. angle? Nice! :)

I knew the minute we met him. It was just a feeling, but the more we got to know him the more momentum it gained.

The only "clue" I got was from my friend telling me that there was a big twist at the end that you'd never see coming. But I got it almost right away. She was so mad xD