Hashem Abedi, 22, collected metal tins and skewers as he allegedly set about fashioning prototype bomb parts before the deadly attack on May 22 2017, the court heard.
Twenty-two people died in the blast in May 2017, including four people from Lancashire.
A small scrap of metal was recovered after his brother Salman Abedi, 22, detonated a homemade bomb, killing 22 people and injuring many more, the Old Bailey has heard.
On Tuesday, jurors heard from Hashem Abedi's former boss and owner of a takeaway food restaurant in Greater Manchester.
The witness, who cannot be identified for legal reason, said in a statement read to the court that the defendant worked as a delivery driver in 2016 and early 2017.
During that time, he had left to work for a "rich friend" in Germany, but returned to resume his cash-in-hand £5 an hour job, the court heard.
The witness said: "I could not rely on him to turn up for his shifts. Hashem was religious but in my opinion he had wrong the idea of Islam.
"He would smoke weed and did not appear honest. I heard him ask other members of staff if he could take cash orders.
"He would tell customers he had no change so he could keep it for himself."
While working for him, Hashem Abedi drove different cars, including a green Nissan Micra, a sky blue Toyota Aygo and a Hyundai, jurors were told.
The witness said: "Hashem asked me if he could take away the empty metal containers from the shop so he could sell them as scrap metal.
"I agreed to this as it meant I would have less rubbish at the shop.
"Hashem would take any metal tins including pasta sauce tins, jalapeno tins and cooking oil tins.
"These brands of cooking oil are sold in large metal tins. We would use approximately one tin of cooking oil a week."
"I believe he would take empty containers from other businesses. I don't think he asked them for permission to do this. I don't know if he sold any of the tins."
The takeaway shop owner said that other staff had told him Abedi's front garden "looked like a pizza shop with sauce tins lying around".
His nephew, who worked at the shop and became friendly with Abedi, gave evidence in court, saying that Hashem Abedi tried to get him to buy sulphuric acid, a key component of TATP explosives of the type used in the bomb.
He told jurors that the defendant had said he needed a large amount of battery acid for a generator at the family home in Libya.
Giving evidence from behind a screen in court, the witness, who cannot be identified for legal reasons, said: "He said something about a generator because there are a lot of power cuts in Libya.
"He said the battery tipped over and he lost the acid and he could not get any acid there because of the war and so he had to sort it out here."
The young man told jurors that he checked it out and discovered battery acid was sulphuric acid and could be bought in small amounts.
He said: "He said he wanted like a large amount. I said I could not get it, you can only get it in small amounts. We never spoke about it again."
The witness said Hashem Abedi had told him he could not buy the acid himself, because his bank account had been closed.
He told the court that the defendant thought he might be able to get a large amount of the chemical through his other engineering work.
Hashem Abedi, originally from Manchester, has denied 22 counts of murder, attempted murder and plotting with his brother to cause explosions.