Could be “anything,” but the first thing Bloomberg thinks of are those who don't like ObamaCare, presumably conservatives or Tea Party activists.
Audio: MP3 clip
From part of Couric's interview with the mayor aired on the Monday, May 3 CBS Evening News:
KATIE COURIC: Law enforcement officials don't know who left the Nissan Pathfinder behind, but, at this point, the mayor believes the suspect acted alone.
MAYOR MICHAEL BLOOMBERG: If I had to guess 25 cents, this would be exactly that, somebody-
COURIC TO BLOOMBERG: A home-grown?
BLOOMBERG: Home-grown, maybe a mentally deranged person or somebody with a political agenda that doesn't like the health care bill or something. It could be anything.
CBSNews.com version of Couric's interview.
****UPDATE: Speaking on Stephanie Miller's radio show, MSNBC's Contessa Brewer offered yet more misguided liberal pontifications on the would-be bomber's motives:
I get frustrated...There was part of me that was hoping this was not going to be anybody with ties to any kind of Islamic country.
...There are a lot of people who want to use terrorist intent to justify writing off people who believe in a certain way or come from certain countries or whose skin color is a certain way. I mean they use it as justification for really outdated bigotry.
Full audio at the link above.