In the lexicon of human loss, it would seem difficult to surpass the story of Fred and Mildred Kassab. Between them, before the time of the "Fatal Vision" killings, they had lost one wife, one husband and four infant children. Fred, a one-time Canadian Army intelligence operator, had lost his wife and daughter in the wartime bombing of London. Mildred, a Long Island interior decorator, had suffered two stillborn pregnancies, lost one child to illness and had, some years into her first marriage, come home to find her husband hanging from the rafters of the garage, a suicide.

This may explain why, when the authorities summoned them to Fort Bragg, N.C., nearly 15 years ago and they learned that their 26-year-old daughter Colette and her two young daughters had been brutally murdered, and that their son-in-law, Green Beret Capt. Jeffrey MacDonald, was the sole survivor, there were no tears.

It may also explain why, upon becoming suspicious of MacDonald, a graduate of Princeton and Northwestern Medical School, Fred Kassab did not rest. After the Army charged, then cleared, MacDonald of the killings, Kassab went to Congress, attempting to contact each congressman personally, demanding an investigation; in the 10 years it took for MacDonald finally to come to trial, he went into debt to counteract his son-in-law's legal appeals. He badgered the Army to allow him into the sealed house where the killings had taken place; he waited for nightfall to sit on the exact couch MacDonald claimed he had been lying on when the murder took place. He became convinced that MacDonald's story of hippie murderers who chanted "acid is groovy" was a fabrication; he almost single-handedly forced a new trial.

Although MacDonald is now serving three consecutive life sentences for murder at the federal penitentiary in Bastrop, Tex., Kassab is still obsessed with the case. He files briefs with the parole board; he leaves work early to talk to the press about the TV movie NBC has made of the case, based on Joe McGinniss' best seller (the conclusion of the two-part movie airs tonight at 9 on Channel 4). He's got to talk to reporters, he says, because every time you look around MacDonald's filed another damn appeal. This case is about the only thing he's involved with anymore.

His role in all this? "Overseer," he says, with a little laugh. But it is a nervous laugh, without joy.

He is talking about the movie that he has now seen three times, and that deals with a murder in which his daughter was stabbed and clubbed repeatedly, the word "PIG" written across her headboard in her own blood, in which his 5-year-old granddaughter Kimberly was clubbed with such force that her cheekbone protruded through the skin, in which his 2-year-old granddaughter Kristen was stabbed 33 times, and a thread of her father's pajama top found under one fingernail.

"It doesn't bother us," he says. "Uh, well, if we could go through 14 years of this -- remember, I had to get deeply involved in this case, right down to reading the autopsy reports and you name it, and then we went through the whole trial -- and if we can do that, we can do anything.

"I really don't think it bothers either my wife or I because there's no mayhem in the movie," he says, hands gripping the armrests of his hotel room chair, elbows stiffly angled. "That's the one promise that we got from them when they wrote the script. One, everything would be authentic on the evidence side. Two, given the subject matter, that it would be in as good taste as possible. In other words, we didn't want to see another 'Amityville Horror.' "

He's a heavyset man, 63 pushing 64, as he puts it, gracious and curiously hearty when first met. He orders drinks for visitors, two Smirnoffs and tonic for himself; he smokes despite emphysema, and coughs. He describes his work, telephone sales for the Quality Egg Co. in New Jersey, supplying frozen liquid eggs for institutional use, like all the eggs for Hellman's mayonnaise. He discusses the case and its effects on his marriage openly, displaying a formidable memory for numbers and names and dates: The one wound in MacDonald's chest was five-eighths of an inch deep; he believes it was 3:40 in the morning when MacDonald first called the police; MacDonald was indicted by the grand jury for murder on Jan. 25, 1975.

But after a while you begin to notice other things. The way he slips back into the details of the case when you ask him how it was when he began to believe that a man he had known for nearly 25 years had murdered his family. The way his voice sometimes trembles. The way this amateur investigator sometimes repeats words not twice but three times, as if the obsessiveness had come to flower in language itself. He says the feelings of sorrow have gotten worse as time passes. "It's been constant, it's been constant, it's been constant," he says.

The mourning, he adds, increased after MacDonald became a suspect. He would much rather it had been a bunch of drug addicts.

"To realize he had done it, and Colette loved him, and when you sit back and picture in your mind's eye what happened that night, with him attacking, and I know from the autopsy reports what was done to the two children, you can't help but visualize it in your mind, though we don't talk about it," he says. "My wife and I can sit for hours and days and not talk to each other, but we're both thinking, you know. And we're very fortunate. Most people who go through traumatic things like this, nowhere near as lengthy, almost always end up in divorce, but with us it's drawn us closer."

Hadn't Joe McGinniss reported in "Fatal Vision" that the deaths had strained the family, that Mildred had stayed up until all hours in their home on Long Island, baking, freezing food for no one to eat, that Fred himself was depressed?

"I think Joe misunderstood a little of that," he says. "The point of the baking, she was keeping herself busy . . . It was for want of something to do. We sort of withdrew from our friends for only one purpose, and that is we didn't want to become a bore to our friends. We had a purpose in mind. We only had one subject of conversation, because it was dragging on and on and on -- we realized that after a while these people are gonna get fed up with us talking about nothing but this. We thought we'd better draw back. We resigned from the yacht club and whatever else we belonged to."

How long did they keep to themselves?

"We're still not back to normal." A dry little chuckle. "We're still not fully normal because this thing hasn't ceased. He's filed for a new trial, there will be briefs, there will be hearings. It just goes on and on and on."

He talks about the tragedies of his life, the incredible statistics, the fact that between him and his wife they have now lost a husband, a wife, five children, two grandchildren and, if you wish to be precise, a son-in-law.

"And that's only part of the story," he says. "My wife and I sometimes say we should have picked up two other people, when you add all the things that happened to us up. It's pretty horrendous. I was wounded six times in World War II, my father died when I was overseas. Of course, Mildred's husband's death was a tragic event, nobody ever knew why he committed suicide, a perfectly happy couple, financially doing well, no reason, she comes home one day and he's hanging. . ."

He is sniffling hard.

"It's terrible. What the hell. You take it one day at a time, it's all you can do. . ."

He is talking about his stepdaughter now, and his wife.

"Mildred had one miscarriage and the second two were stillborn and they were all 'Colettes,' " he says. "So Colette, when she was born, actually had three birth certificates. . ."

"She wanted a baby girl the worst way. I did too," he says. "I like little girls. Of course, Colette and I were very close. She would never allow anyone to call me her stepfather, always her father . . . She was 12 when I met her mother, 13 when we got married. Her brother Bobby was four years older . . . She was the type of girl -- the best way I can explain it, I never met a girl that did not like Colette. She was a pretty girl, not beautiful but pretty, and she was down to earth and she hated to see anybody hurt. I always remember the kid next door had polio -- Colette used to walk her bike to school with him so he wouldn't have to go to school alone."

Colette met Jeffrey MacDonald -- handsome, athletic, intelligent -- when they were in eighth grade at Patchogue Junior High School on Long Island; they married when both were in college after she became pregnant. After graduating from medical school, MacDonald joined the Army; he volunteered for the Green Berets and was disappointed when he was sent to Fort Bragg instead of Vietnam. By all accounts, they were a happy family. For Christmas in l969, when Colette was pregnant with their third child, and the Kassabs were visiting, MacDonald gave his children a pony -- the first step in their dream of one day living in the country. Less than two months later Colette and the children were dead. MacDonald, in his hospital bed recovering from a punctured lung, told investigators he'd wrestled with drug-crazed intruders and spoke of a blond girl wearing a floppy hat and a hippie who knocked him cold.

When the Army later charged MacDonald with the killings, Kassab was, he says, one of his biggest defenders. He had always thought Jeffrey was "a nice boy," he says. "Matter of fact, if you were to meet him now you'd think he was the most charming person that ever was.

"He can charm the birds right out of the trees," he says now. "A true psychopath."

After a four-month investigation, the Army dropped the charges.

Kassab had no reason to doubt his innocence.

Except for one thing. In November 1970, after MacDonald had been cleared, he called up Kassab and told him that he had gone out with some of his buddies, looking for the people who had killed his family, and had found one and murdered him.

"At first I believed him," says Kassab. "Then I stopped to think how ridiculous it was . . . The FBI had people all over the country and nobody finds anything, and here it is one night this man goes out and finds them. He said the body had been found by the police, and they thought it was robbery or something . . . I went down and investigated it. I got every paper in a 50-mile radius, and there had been only one murder that night, and the police had the guy who did it in custody, so I figured the whole story was ludicrous." It was the beginning of the end of his faith in MacDonald.

That December Kassab obtained a copy of the transcript of the Army proceedings and found that MacDonald's story "didn't hold water -- it got worse and worse and worse." Suspicious, but still determined to proceed cautiously, he traveled to Washington to request Congress to reopen the case.

"I figured if I said my daughter and grandchildren had been murdered, they would pat me on the head and say they were sorry but there was nothing they could do about it," he says. "So instead I drew up this 14-page document of all the ways the Army had loused up the case, took them down to Washington in two of the biggest suitcases you ever saw, and proceeded to hand-deliver them to every congressman and senator."

Following hearings by congressional committees, the Army reopened the case. Kassab kept rereading the Army transcript. In April 197l he received permission to enter the sealed apartment with investigators, and found that despite the terrible battle MacDonald had described, only a coffee table was upset in the living room and a bedroom lampshade slightly crooked. He learned that the blood type of every member of the household was different, "so that it was very clear who bled who." When at last he walked out of the house, says Kassab, "there wasn't any doubt in my mind that he was guilty."

And what is it like, this realization that a man you have known for so many years has murdered your child?

"Well, it's shocking . . ." Kassab begins, before seeking refuge in evidence.

"It's a terrible emotional sensation, and to make it worse, I've been defending the SOB for over a year . . ." he says a second time.

"Well, your initial feeling is you want to go out and kill the SOB," he says, a third.

There were long legal battles before MacDonald finally came to trial, in 1979, and was convicted of first- and second-degree murder. It took the jury six hours to convict him, his former staunch supporter says. Including the one-hour break for lunch.

He's trying to do, now, the undoable, to describe, within a two-hour conversation, the effect of this murder. You will excuse him if, during this conversation, he finds it necessary to turn his back, and go to the ice bucket, and linger for some time, ostensibly refreshing his drink.

"The only way I can put it into words, in our particular case, it wrote 'Finito' on our lives," he says. "Because, uh, at this stage in the game, I could care less if I drop dead tomorrow -- my wife, too. As long as he's in jail, we're satisfied. I'll give you an idea . . . My wife got cancer, in 1971, she wouldn't tell anyone, she wouldn't tell me, she got a big lump in her breast and she wouldn't go to the doctor, she just figured the hell with the whole thing. Finally, I found out. I made her go to the doctor, pointed out she was being selfish, I needed her to help me. They operated the next day. She had a radical mastectomy, they didn't get it all, they did cobalt treatment . . . She's fine now, but that will give you an idea how she felt . . ."

He rises.

"It's just, both of us have had too many things to cope. You say, 'Hang the whole thing' -- can I get you a little more?"

But he's still here.

"Oh, I'm not the suicide type," he says, "But we've all thought of it. . ."

He's still working.

He laughs.

"I can't afford to stop working, I have to work to eat. . ."

He lights a cigarette, coughs.

"My nerves just get the best of me," he says. "It's a funny thing. I'm able to do all these TV interviews, I had done pretty good with them, but afterward, when it catches up with you, it's like a delayed reaction . . . like a terrible letdown."

Like a depression?

"Yeah."

So why do it?

"To counteract this public relations thing of [MacDonald's]," he says. "He's got people all over the country supporting him. He's got doctors at the hospital where he used to work donating one day's salary every month to him. He's filed an appeal for a new trial -- he has as much chance of getting a new trial as I have of flying without an airplane, but he's filed. . ."

The ice in the drinks shifts. The talk turns to what can happen in the space of 25 years.

Well, he would say, he doesn't have the stamina he once had. On the other hand, he is adamant that MacDonald stay in jail. He is so adamant that he has filed a letter with MacDonald's parole board, for that time when he becomes eligible for parole.

"April 5, 1991," he says, rattling off another date. "I went on record with the parole board to document the reasons I thought he shouldn't get on parole, because I'm assuming in 1991 I'm not gonna be here and therefore I want to be heard."

In other words, there will not be an end to this battle.

In other words, even death will not prevent him from seeing this battle through.