I doubt it was Al Qaeda. The huge cloud of white smoke strongly suggests the explosive was (sulfurous) gunpowder. Al Qaeda bombers are far too advanced to use something that primitive. They know how to make ANFO, which is basically what Timothy McVeigh used in Oklahoma City. That would have caused ten times the damage of yesterday's bombs.
pressure cooker bombs such as this have been used in Afghanistan, Pakistan, India, Nepal, etc. And the Ft. Hood bomber did as well.
The pressure cooker is basic and common. It serves only as the containment for the explosive material, which is the critical component.
If gunpowder was used, which all that white smoke would suggest, the people in the area of the blast were very lucky. Because gunpowder is comparatively slow-burning. But everything I've read or heard about Al Qaeda bombers is they use ANFO or C-4, either of which would have produced infinitely more damage.
So far my guess is some homegrown, unaffiliated, sympathetic fanatic(s) did this. But time will tell.