The trap was set. All that was left for Los Angeles County sheriff’s investigators to do was wait and see if the unthinkable was true.

Suspicions had grown that one of their colleagues — a respected captain with more than 150 deputies under her command — was funneling secret information to an alleged Compton drug trafficker. So investigators sent out a phony plan as bait, according to records and interviews, detailing their intention to do surveillance on a house near the suspected trafficker’s home.

A few minutes after receiving the fake plans, Capt. Bernice Abram was heard on a phone tap placing a call to Dion Grim, the suspected drug dealer.

Authorities listened in as she tipped him off about the location of the planned surveillance. Stay away, she warned.

That day, in April 2011, sheriff’s officials placed Abram on leave, and for more than a year afterward her ties to Grim were investigated. Prosecutors recently declined to file charges against Abram, saying they couldn’t prove the captain knew that Grim, a documented gang member, was involved in illegal activities.

But a district attorney’s memo explaining that decision provides the most detailed description yet of how the Sheriff’s Department came to believe one of its up-and-coming leaders was betraying the agency and shows the efforts officials pursued to prove it. The memo also documents several occasions when Abram appeared to use her authority to help Grim avoid law enforcement scrutiny.

An FBI investigation into Abram is ongoing, a spokeswoman said.

The Sheriff’s Department placed Abram on leave along with her niece, a custody assistant who prosecutors said improperly accessed a law enforcement database for Grim. They remain on leave and together have collected more than an estimated $300,000 in salary as the sheriff’s internal probe continues, based on posted county salaries.

Abram first met Grim after she started dating his father three years ago, prosecutors said. (According to her Sheriff’s Department biography, Abram, 53, was married to another man.) She became “good friends” with Grim, 36, a member of the Original Front Hood Crips, a Compton street gang.

In 2010, FBI agents had begun investigating Grim, suspecting that he was the ringleader of a cross-county drug trafficking ring. A sheriff’s detective helping with the investigation was reviewing Grim’s wiretapped phone calls when he heard a woman’s voice he recognized: Abram’s.

In the months that followed, authorities continued to target Grim. And on several occasions, Abram interjected herself, prosecutors said. In one instance, a sheriff’s deputy, Michael Haggerty, was directed by the FBI to arrest Grim after a traffic stop. In an interview with The Times, Haggerty described Grim as oddly calm for someone in the back seat of a patrol cruiser. “You’ll see what happens,” Grim said, according to the deputy.

The district attorney’s memo details Abram’s involvement in the case: Shortly after the arrest, she called the Compton station and asked for Grim to be quickly released from custody. She got his car out of impound and got the fees waived. She also picked Grim up from jail, according to the memo.

Days later, she texted another deputy at the Compton station who considered her a mentor, asking if he knew Haggerty. She told him Haggerty had issued a ticket to a family member of hers and that the court date was approaching. “Feel him out,” she reportedly said.

The deputy then approached Haggerty and told him that a friend from the Carson station “who had a lot of clout asked him not to show up in court if he was issued a subpoena,” according to the memo. The city attorney dismissed the case, however, so Haggerty was never subpoenaed.

Around that time, the Sheriff’s Department began receiving multiple citizen complaints against Haggerty. One of the complainants, the memo states, “admitted that Abram instructed them to make complaints to get Haggerty transferred” out of Compton.

A few months later, another sheriff’s deputy arrested Grim on an excessive noise violation. Again, according to the memo, Abram called the station to get Grim released. This time, she asked that he not be moved to the jail and instead be kept at the station, where she picked him up. She was heard later on the wiretap assuring Grim the case wouldn’t be filed. “I told someone he’d better take care of it,” she said.

The month after that, a deputy at Abram’s station ticketed Grim’s sister on a traffic violation. Abram approached the deputy and “asked him to make the ticket ‘go away,’” according to the memo. She later used her power as a captain to void the ticket.

The favors continued, according to prosecutors. In January last year, Grim called Abram to ask about police activity on his street. She called back minutes later and told him that sheriff’s gang enforcement deputies had served search warrants targeting two shooting suspects and planned to serve another the next day.

A few months later, Grim was ticketed again, and he immediately called Abram. She ordered a detective at her station to “look into it,” according to the memo, an order he understood to mean that he should get the ticket dismissed.

That month, sheriff’s investigators moved in with their sting operation, ensnaring Abram with the phony surveillance plans. She was relieved of duty, along with her niece, Chantell White, a custody assistant at the sheriff’s South L.A. station. Investigators discovered that on three occasions, Grim used White to access a law enforcement database to run a friend’s name for outstanding warrants, according to the D.A.'s memo.

Last year, federal authorities arrested Grim and several other alleged members of a drug ring suspected of moving marijuana, Xanax pills and pint bottles of codeine with promethazine, also known as “sizzurp” or “purple drank.” Grim has pleaded not guilty.

Both Abram and White have repeatedly declined to comment to The Times. In one instance, Abram told a Times reporter before hanging up that she’d never heard of Grim.

Prosecutors gave several reasons for not filing charges against Abram and her niece. It’s illegal for police to alert anyone of a warrant before it’s served, but only if the purpose of the warning is an attempt to help prevent an arrest or a search. In one of the instances in which Abram warned Grim, he wasn’t the subject of the warrant, and she had advised him to make sure his children were inside, an attempt to keep them out of harm’s way, prosecutors said.

As for Abram’s second tip, when she warned Grim about the phony surveillance operation, prosecutors also concluded no laws had been broken. The D.A.'s office said there is no evidence that Abram was aware of illegal activities by Grim, who prosecutors noted in the memo worked at a trash collection company.

Prosecutors, however, did conclude that Abram broke the law by quashing a ticket for Grim’s sister and trying to quash a ticket for Grim. But the one-year statute of limitations for that misdemeanor had expired. The district attorney’s office also determined that White may have broken the law by giving Grim information from a law enforcement database, but the statute of limitations on that misdemeanor had also expired.

robert.faturechi@latimes.com