They found multiple devises.
Which means it wasn't a suicide bomber.
I still favor the suicide-bomber possibility.
From the videos I've seen, the explosion (or one of them) took place behind or under the stands, right next to the finish line.
Hard to believe that a vehicle with a bomb could get in there without being stopped and inspected.
Ditto for an unidentified object being left on the ground in that location without arousing suspicion.
Only other thing, it seems to me, is a person with a suicide bomb belt under his clothes. That could have been coordinated to go off at a certain time, or maybe by a radio signal, along with other devices.
If so, there won't be much left to put on trial. But could he have operated alone? Where did he get the explosives? Who, if anyone, helped him?