France had a sleeper cell who planned to use Pressure Cooker Bombs.
However - this sounds very much like the traditional two arseholes who enjoy the life they have but romanticise and obsess about ideology. They feed each others obsessions, likely studied it all together, planned together and finally carried it out together.
Doubt they're a sleeper cell; but they do exist.
I think that's a fairly good analysis based on what we know so far
God, this is torturous. Hope they find the shithead and bring him in alive.