Kallstrom was a top electronic surveillance expert for the FBI. Here is what the New York Times wrote about him in February 1995, when he was appointed to head the FBI's New York City office:
A former Marine captain and a Vietnam veteran, Mr. Kallstrom joined the F.B.I. in 1970 and spent most of his career in New York City, heading the unit responsible for electronic monitoring of criminals.
As the head of the Special Operations Division in New York from 1976 to 1990, Mr. Kallstrom oversaw a band of surveillance experts that grew from 15 to more than 300.”A little less than three years later, Kallstrom retired from the FBI to take a job with MBNA Bank. During his tenure as director of the New York City office, Kallstrom presided over the controversial criminal investigation into the 1996 crash of TWA flight 800.
In a presumably unrelated incident, Kallstrom was a strong advocate of the innocence of FBI agent, Lin DeVecchio, who was indicted in 2007 on charges of helping Mafia informant, Gregory Scarpa, commit four murders in the 1980s and 1990s. Charges were dropped when it was revealed that the government's key witness, Scarpa's mistress, had given conflicting accounts of DeVecchio's involvement. Information Scarpa supplied to DeVecchio played a major role in the "Mafia Commission Case" that established the reputation of young prosecutor Rudy Giuliani in 1985.
There are provocative "conspiracy theories" having to do with Kallstrom's involvement in the TWA flight 800 investigation and its relation to the DeVecchio case. I won't link to them because anyone who wants to know can simply Google the key words. The truth is out there -- so is a lot of speculation and innuendo. What is unequivocal, though, is the relationship between FBI investigations and informants of dubious character. A December 1996 New York Magazine article featured the Scarpa/DeVecchio relationship without going too deep down the rabbit hole of conjecture.
UPDATE: See also the December 16, 1996 New Yorker feature, "The G-man and the Hit-man" from which the following:
In 1980, the Department of Justice had issued detailed guidelines: if an informant was suspected of involvement in any “serious act of violence,” the supervisor in charge was required to consider closing him and targeting him for arrest. While it was understandable that DeVecchio might be reluctant to close a top-echelon informant --particularly someone who had helped make his career [S: and that of Rudy Giuliani] --that seeming reluctance put him at odds with some of his own agents. Eventually, four of them reported to the Bureau that, in an apparent effort to protect Scarpa not merely from arrest but from his enemies in the Mob, DeVecchio had leaked sensitive, confidential information to him. One agent has alleged that DeVecchio became compromised to the point of helping Scarpa locate people that Scarpa wanted to kill.
In early 1994, DeVecchio was placed under investigation, but in the meantime he was neither discharged nor put on administrative leave. Instead, he was moved off his squad to another supervisory position -- as the F.B.I.’s drug-enforcement coördinator for the entire Northeastern United States, with unrestricted access to classified documents. He continued to hold that job after he informed the Bureau in a sworn statement that he was not amenable to a voluntary polygraph examination, and, incredibly, even after invoking his Fifth Amendment privilege and refusing to testify about his conduct as an F.B.I. supervisor at a hearing last May. No F.B.I. official—not even Louis Freeh or the New York chief, James Kallstrom—would comment on why a man being investigated for leaking information was kept in a post requiring top-security clearance. Douglas Grover, DeVecchio’s lawyer, says it is because the Bureau had always understood what DeVecchio was doing to protect a valuable informant, and had approved of his actions. “Whatever Lin did, he did it as an agent of the institution, both literally and figuratively, acting on behalf of the F.B.I.,” Grover says.