Bellingham left Birmingham City over a year ago for Dortmund.
Edu took over from former head of recruitment Sven Mislintat in 2019 with high-profile scouts Steve Morrow and Francis Cagigao among those to be moved on.
Adams recalled to Sky Sports: "I think it (a deal to sign Bellingham) got lost, this one, in the transition of the chief scout at Arsenal going out.
“He was spotted very early on, not by me, by the Arsenal recruitment office. The chief scout was absolutely bowled over by him and the great prospect that he is.
“He had more or less done the deal but at that moment the new sporting director Edu came in from Brazil and had no European experience and no UK experience.
“And I think it got lost in the transition, Edu didn't know anything about this player. Unfortunately, the chief scout had the deal kind of done.
“We missed that one, unfortunately. They are the type of players we need to get hold of at the Arsenal if we're ever going to develop and go forward.
“These kinds of players we need to tie up and get them to the Arsenal and build a phenomenal league team. He's a great talent but unfortunately, he's not joined the right club."
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