The fact that the Kings County district attorney is dealing with two cases of possible ethics lapses by his staff is eliciting warnings from specialists that the prosecutor in the city’s biggest borough may need to review internal protocols and training.

In one case that surfaced this week, a detective investigator began a romantic relationship with a potential witness in an organized-crime case and allowed the potential witness to break the conditions of his temporary release. A spokesman for the Brooklyn district attorney’s office, Jerry Schmetterer, said the investigator has since retired from her position, but that the FBI is investigating the case.

In the other case, an assistant district attorney allegedly leaked sensitive documents to her fiancé, a criminal defense attorney. She was suspended last week and the Queens District Attorney, Richard Brown, has been asked to act as a special prosecutor, Mr. Schmetterer said.

The Brooklyn district attorney, Charles “Joe” Hynes, was first elected in 1989 and is in his fifth four-year term. He has recently attracted attention for winning convictions of a former assemblyman, Clarence Norman, who was the chairman of Brooklyn’s Democratic Party. Mr. Hynes won a victory in 2005 in a Democratic primary with 47,998 votes of 115,119 cast. His closest challenger, John Sampson, received 42,337 votes. There was no serious Republican challenge in the general election.

“Two in a row is something that Hynes should be deeply concerned about,” a law professor who specializes in legal ethics at New York University’s School of Law, Stephen Gillers, said. “There has to be protocols in place to avoid just this sort of thing.”

Mr. Gillers said he was speaking hypothetically because he had no specific knowledge of the two cases.

The detective investigator, identified as a 17-year-veteran of the District Attorney’s office, Maria Biagini, was assigned to protect a low-level con artist with organized crime ties while he was interviewed about the ongoing corruption case involving a former FBI agent Lindley DeVecchio. DeVecchio was indicted last year on four murder charges. He allegedly provided information about informants to the Colombo family crime boss, Gregory Scarpa, which led to the murders.

Ms. Biagini fell for the man and allowed him to break the conditions of his release by contacting his family and throwing dinner parties, according to an article in yesterday’s New York Post, which first reported the story.

Federal agents monitoring the man’s mail once he returned to prison, where he is serving the remainder of a larceny sentence, uncovered letters from Ms. Biagini that disclosed their relationship, sources said. One letter proposed a scheme where he could visit a fertility clinic so that she could become impregnated while he was still in prison, according to the New York Post article. Ms. Biagini couldn’t be reached yesterday.

The FBI is now leading an investigation into her alleged actions, which could result in criminal charges.

The second case is focusing on an assistant district attorney in the domestic violence division of the Brooklyn District Attorney’s office, Sandra Fernandez. She was suspended last week after an internal probe revealed she had leaked documents to her fiancé, criminal defense attorney Douglas Rankin. Ms. Fernandez could not be reached and calls to Mr. Rankin’s office and home weren’t returned yesterday.

The suspension was first reported in the New York Law Journal yesterday.

Another assistant district attorney first became suspicious of Mr. Rankin, who is representing a client in a gang-related robbery case, when he was questioning a witness in his case earlier this month, sources said. Mr. Rankin started waving documents in front of the witness, telling him that he had proof he was lying, sources said. The assistant district attorney then began investigating how Mr. Rankin received the documents and traced them to Ms. Fernandez, who had accessed them through a computer, sources said.

The Brooklyn District Attorney’s spokesman, Mr. Schmetterer, said he couldn’t comment on the case other than to confirm that Ms. Fernandez had been suspended.

“These are two bizarre cases,” he said. “I don’t think any conclusion can be drawn yet… If the investigations bring out some problems that we need to address, we’ll address them.”

A law professor at Pace Law School who has written about prosecutorial misconduct and legal ethics, Bennett Gershman, said Ms. Fernandez could lose her law license and face criminal charges if she is proven guilty of leaking documents. Other legal experts said Mr. Rankin could also risk losing his law license if it is proved he received documents that he knew were improperly acquired.

“Leaking documents is as bad as it gets. You could be compromising investigations, the safety of individuals,” Mr. Gershman said. “Those kinds of relationships and entanglements — you hope they are screened out before a person gets into the office and that they have the integrity to play it straight.”

“These are two serious incidents and occurring at the same time suggests that there may be a problem in supervision and training in that office,” he said.