Stuffed to overflowing are the annals of mayhem television produced behind the all-justifying shield "Based on a true story." ABC offers another entry as its Sunday night movie, at 9 on Channel 7: "A Killer in the Family," a film that is powerful, yes, and quite gripping, and well acted, and all of that, but depressingly unnecessary when all is said and done.

Robert Mitchum, in a role more suited to his screen persona than the old moose he played in "Winds of War," stars as the convict father of three teen-age boys who convinces his sons they must help him break out of prison because his life has been threatened by fellow inmates. They think of Dad as somebody who just "did something stupid" years ago (he stole a car, embezzled money and killed a security guard, we are belatedly told) and of springing him from the Arizona State Prison as an act of familial obedience and love.

Once sprung, however, Papa slowly reveals his true colors, those of a vicious amoral sociopath, and the adventure turns into a nightmare when the old man and his accomplice (Stuart Margolin) cold-bloodedly murder a family of four, including a baby, after stealing the family's car as part of the getaway.

The shooting occurs off-camera, but the film is preceded by a parental advisory which says the script (by Sue Grafton, Steven Humphrey and Robert Aller) is based on "court transcripts, investigative reports and interviews" and that the film includes "incidents of uncommon violence." It can be argued that such alleged advisories are really titillating teases in disguise.

Gerald Fried's opening music suggests an American dream gone perversely awry, but that's about it for social context in the telling of this story. Director Richard T. Heffron contributes a fairly deft trompe l'oeil irony at the beginning (one thinks this is an ordinary family gone on a picnic--but then the camera pulls back . . .), but once that's over, the film is just bare narrative, a study in the growing panic among the boys and the eventual and inevitable tragic end to their flight.

Mitchum is again the imposing brute, as in so many other films in which he has appeared, and we share the growing awareness of his sons that the man is dangerously deranged. The sons are played by a trio of impressive young actors: James Spader as Donny, the oldest and most skeptical; Lance Kerwin (once "James at 15") as Ray; and Eric Stoltz as Ricky, the one most reluctant to abandon faith in dad. Lynn Carlin and Salome Jens also make brief appearances.

"I wouldn't make judgments 'til you find out what you're capable of yourself," the father lectures his sons at one point, and much later they hear the Margolin character say of good ol' dad, "He'd kill you in a New York minute." The story of the sons' disillusionment, and growing horror, is compelling up to a point, but the film never makes the big reach to anything large or significant, and since it is dealing with unsavory lives, on network television, it really needs to make that reach.

"A Killer in the Family" ends up being commentary on not much more than the kinds of roles usually played by Robert Mitchum.