Caution is warranted, but DHS put out an internal memo - published by Fox - that says the following:
[S]trong suspicion is being directed at AmRen / American Renaissance. Suspect is possibly linked to this group. (through videos posted on his myspace and YouTube account.). The group’s ideology is anti government, anti immigration, anti ZOG (Zionist Occupational Government), anti Semitic. Gabrielle Gifford is the first Jewish female elected to such a high position in the US government. She was also opposite this group’s ideology when it came to immigration debate.
Duly noted. On a factual basis, it seems to me that by far the most important possible clue is that the police say they have been looking for an accomplice. If that pans out, then we have something more than a lone deranged figure.