That's a photo of the killer, Tomohiro Kato, 25 (Japan Probe.) Mianichi reports that Kato may have been angered some time before his rampage, when his work clothes went missing and he assumed he had lost his job:

"My work clothes are missing!" the suspect, 25-year-old Tomohiro Kato, shouted at the Higashi-Fuji factory of Kanto Auto Works, Ltd. at around 6 a.m. on Thursday, shortly before his shift began, prompting a colleague to alert their boss. He had disappeared by the time the boss arrived at the scene.

Later in the day, he put up several messages on a mobile phone site complaining about what happened at the factory.

"When I went to my workplace, I found my work clothes were missing. Does it mean I should quit my job?" one of the entries read.

"I guess the company is happy about expelling me," another messages said.

Investigators suspect that Kato thought that he had been dismissed from the factory.

They also report that Kato had been posting several other angry messages from his phone and on 2chan before the killings. The messages map his progress over six hours as he travels to Akihabara (translation via Patrick Macias):

am 5:21 I'm going to kill people in Akihabara. I'll crash into them by car, and when the car is down, I'll use my knife. Goodbye everybody
am 5:21 sleepy
am 5:34 I still have headache
am 5:35 weather man says it's a rainy day. Worst.
am 5:44 The worst case is that I'll get caught during(the killing spree)
am 6:00 I'm not being cheated, maybe I am the one who cheats
am 6:02 I'm used to play a good guy. Everybody believe it so easily.
am 6:03 Adults liked me, since I am "a good kid".
am 6:03 Couldn't make any friends
am 6:04 still, there were few who got along with me
am 6:05 Some of them kept me in their mailing list, that makes me feel good a bit
am 6:10 The road I was to take is sealed. Everything is against me
am 6:31 It's time. Let's go
am 6:39 I have to fight my headache
am 6:49 and the rain
am 6:50 and the time
am 7:30 I did my homework perfectly and look at this rain
am 9:41 I hope the weather gets better
am 9:48 Now I'm in Kanagawa. resting. Everything is fine so far
am 10:53 Heavy trafic jam. Dunno if I get there on time
am 11:07 Shibuya sucks
am 11:17 It is sunny around here
am 11:45 arrived on Akihabara
am 11:45 Hokoten today, isn't it?
pm 0:10 Now it's the time

Kato then drove his two ton truck (that's a big truck, by the way), running over three people before jumping out with a knife. From the Washington Post:

When the rental truck barreled into the street, the area was crowded with pedestrians. Kato quickly got out of the truck with the knife and headed directly for one of the people he had run over, witnesses told reporters.

Kato "jumped on top of a man he had hit with his vehicle and stabbed him with a knife many times," one man told the Kyodo news agency.

Kato, wearing a white jacket and a black T-shirt, screamed and grunted as he stabbed people, according to witnesses, some of whom said he appeared to be mentally disturbed.

According to Danny Choo:

Witnesses said that Kato had a frenzy look on his face and that he looked like he was enjoying his killing spree.

An officer chased Kato down an alley and tried to apprehend Kato with a stick. Kato started to scream and shout until the police officer pulled out his gun and said "I'm going to shoot!" where upon Kato collapsed to the ground and gave himself in.

After he was apprehended, he was quoted as saying:

"I am tired of life," police said Kato told them later. "I came to Akihabara to kill people. It didn't matter who they were. I came alone."

Danny also points out the creepy “Anyone would have been fine” statement, listing three other recent attacks in which the perpetrator used those same words.

Finally, Marxy posts his own thoughts, resulting in some of the best, and dare I say insightful conversation in the comments. One comment points out that apparently a police officer was chasing Kato while he continued to stab people, only pulling his gun after Kato surrendered. Also, pop band AKB48 (who are named after and perform solely in Akihabara) apparently went on with their show without any acknowledgment of the incident. It would seem that much of the media is focusing on an extremely thin connection to anime and manga (despite practically everyone ever through the history of time doodling pictures in the margins of the school notebooks/cave walls) and even possibly video-games (with zero proof) and yet talking not-at-all about possible mental illness.

Plenty of people will be beating their chests and waving their own moral flags over this one for a long time. Personally I find there is very little to say.