If the devices were not armed and able to detonate, that further narrows the field of suspects.
That would put the suspicion clearly on the left.
If fully functional, just not yet detonated...it’s likely the right.
And let’s not forget “The Russians” (my term for any foreign state actors). They just like to stir the pot and turn up the heat.
I rule out Islamists and others of that type.
Islamics would have got the job done..and with collateral damage.