Despite uncovering a major pot-growing operation hidden behind the walls of a maraschino-cherry plant last month, Brooklyn District Attorney Ken Thompson dived immediately into another probe — to find out how his investigators could have botched the raid so badly, sources told The Post.

That’s because Thompson’s detective investigators failed to search the “Breaking Bad”-style business owner — allowing him to walk around during the daylong raid with a .357 Magnum strapped to his ankle. He used to kill himself, but could have used on the raiders.

“When the incident happened, everything was scrutinized and everyone was questioned,” said a law-enforcement source.

Arthur Mondella, 57, wasn’t frisked when the search began and was able to walk into his office bathroom and shoot himself in the head immediately after detectives found the entrance to his massive underground pot farm on Feb. 24.

Thompson’s probe found that his investigators had failed to search Mondella, potentially imperiling the case and putting more than a dozen environmental and DA investigators on the scene at risk.

“An internal investigation found that more than one DA detective investigator made missteps,” said a law-enforcement source.

Thompson never issued a press release about the raid, and his office has declined to comment about it.

The probe concluded that the DA’s office’s missteps included not alerting the accompanying environmental agencies before the search that Mondella had a gun permit and — most importantly — not searching him, sources said.

As The Post reported Wednesday, Anthony Schembri, the veteran DA investigator who was the “case officer” on the search, was forced to resign after being questioned about both the botched search and about leaks to reporters.

A DA spokeswoman declined to comment.