Kallstrom was “sickened,” he recalled to NEWSWEEK. The Kallstroms had been “great buddies” with the Christophers for as long as they could remember–they’d double-dated and played with the Christophers’ 12-year-old son. Now Kallstrom finds himself the man in the middle of the government’s anxious efforts to solve the mystery of Flight 800. Last week, despite the official position that the case was open, Kallstrom more than hinted that he suspected a bomb–a sign that he’s ready to get on with building a criminal case.

Grappling with a personal loss while he directs one of the most extensive FBI probes in history is difficult for the stocky, 53-year-old former marine captain. Kallstrom is particularly pained when the victims’ families complain that investigators like him aren’t doing enough. A few nights after the crash, he went to JFK Airport to confront them. “I felt like I was one of them,” Kallstrom said. “I told them one of my very close friends had been on the plane.”

Since the crash, Kallstrom has rarely left the bureau’s Master Command Center in Manhattan. On top of choreographing the hundreds of agents working on the case–and delivering six progress reports a day to to his boss, FBI Director Louis Freeh–Kallstrom has taken over the marathon daily press briefings. He’s been working around the clock, sending home for clothes and allowing himself only occasional catnaps on his office sofa. (He has finally agreed to take a room in a nearby Marriott.)

Kallstrom is accustomed to painstaking police work. Signing on with the FBI in 1970 after heavy combat tours in Vietnam, he was soon detailed to the organized-crime task force in New York, where he met Freeh, then a young field agent. The two forged a friendship that grew tighter as their careers intersected. For years Kallstrom was one of the FBI’s electronic-surveillance wizards. He headed up the Special Operations Group, the legendary “second story” men who slip into homes and offices in the middle of the night to plant court-ordered phone taps and bugs. Kallstrom once tucked a video camera inside a fire hydrant to watch a mobster’s front door. His stealthy mikes helped nab some of New York’s best-known capos, from the “Pizza Connection” bosses to John Gotti. Freeh became director in ‘93, and he made Kallstrom his top man in New York last year.

All those mob busts took time, and Kallstrom is equally ready to invest whatever it takes to solve the TWA case. “We’ll figure out who did it and where they are,” he told NEWSWEEK. The way Kallstrom sees it, he owes Janet Christopher nothing less.