British police have now announced that the Manchester suicide bomber did not have aid in manufacturing his device, all 22 people originally taken into custody without charges being filed:

Manchester bomber Salman Abedi was likely to have built the device that killed 22 people alone at his flat, police have said.

Officers said there was now a “deep understanding” of Abedi’s movements in the weeks leading up to the attack.

The head of counter terrorism said it was “less clear” whether he had obtained and stored all the materials or if others were “complicit”.

All 22 people arrested over the attack have been released without charge.

Det Ch Supt Russ Jackson said Greater Manchester Police now had details of Abedi’s movements in the weeks leading up to the Manchester Arena bombing.

These included how the chemicals to build the bomb were obtained and where he put the device together.

Reports are that the bomber used the explosive TATP, which seems to be a favorite of would be bombers because:

• Instructions on its manufacture are easily available on the internet. (Don’t Google it. You will probably end up on some TLA’s watch list)
• Its precursors are readily available, and their purchase does not raise red flags as a result.
• Manufacture is less difficult than making beer from from the original grains.
• It is not detected by common explosive detection, because it contains no nitrogen. 

I would however note that TATP what is best described as some truly nasty sh%$, as it is extremely unstable, and even if you don’t accidentally blow yourself up, it degrades over a relatively short period of time without some sort of post processing with a stabilizing compound, so its use in conventional military or commercial explosives applications are extremely limited.

Still, it’s just about perfect for a not particularly well trained lone wolf suicide attacker, because it’s an easy to make yourself dead with a very loud noise.