Surprising laughs at inappropriate moments during Monster must have come from nerves and not the funny bone, but most eyes could not have been dry by the end of this movie. Not that director/scriptwriter Patty Jenkins' powerful début is a tearjerker -- far from it. Nor is it a thesis social statement movie like soon-to-be-released anti-capital punishment Aileen: The Life and Death of a Serial Killer, whose directors Nick Broomfield and Joan Churchill supplied information and outtakes from their work. Ditto a "love story," as one of the five co-producers would have it.

Rather, Monster is that rare type, a finely done film that engages an audience despite a protagonist who is despicable and whose two or three acts of relative generosity pale alongside heartless cruelty. Some found humor in Donna Tentler's (Annie Corley) platitudes that life's tough breaks do not warrant immorality -- and she doesn't know the half of it --but no amount of hard knocks could excuse the acts of Aileen Wournos.

A first Florida john (Lee Tergesen) who attacks, binds and sodomizes hitchhiking prostitute Aileen/"Lee" (Charlize Theron, who also co-produced) is repellent, and his shooting death is self-defense, and another client, pitiful stutterer and virgin Gene (Pruitt Taylor Vince), is left unharmed; but even imagined job-application insults and the prurience of some cops are swept aside in the last murder, circumstantial as its motivation is, of a kindly retired police officer with a crippled wife and grandchildren.

This is no sob-story "let's-feel-sorry-for-the-serial-killer movie. When you just tell the truth . . . you do arrive at empathy." The plotline, "Based on a True Story," is that of the notorious "man-hater" (so the press says) who in 1989-90 took six or seven lives, depending on your source, spent twelve years on death row and, at her request, was executed October 9, 2002. Whereas Broomfield's 1992 Aileen Wournos: The Selling of a Serial Killer centered on the first trial, and his and Churchill's latter documentary covers largely from final appeal to lethal injection, Monster is a more personal, hence emotional, portrait. Twelve hours before the end, the condemned woman granted Jenkins access to ten years' worth of voluminous personal correspondence, which letters serve as starting point.

That it works, and works so well, is due to a sensitive yet objective script and, most importantly, to the performance of Theron, unrecognizable with added soft body weight, irregular teeth, brown contacts and splotched freckled skin makeup by Toni G. Looking more like photos of the real Aileen than her own self, the transplanted South African actress walks a skillful line between extremes of overplaying her hand and seeking justification as a victim.

So commanding is Theron that she overshadows the usually dependable Christina Ricci as wimpy manipulative Selby Wall, the pixieish lesbian who becomes friend, lover, cause, raison d'être and, at the last, cowardly betrayer. Based on fact as we know it but with the name changed (from real-life Tyra Moore), the broken-armed, whiny "Selb" is freed by Aileen, less theatrically than James Cagney for Rev. Pat O'Brien and the Dead End Kids, with a subtle glance; in her defense, it is the younger woman's rôle here to be protected, dominated, spared. Aileen's sacrifice -- for love -- is consistent in the midst of inconsistency, and admirable even as the "martyr" is to remain abhorrent.

To strip malls, biker bars, fun fairs, convenience stores, second-rate motels, highways and dirty overpasses, the tale works out to a conclusion that is foreknown but holds the viewer's attention. Sharp focus on Aileen, and Selby, is cut only by two interludes of disinterested friendship from self-storage manager Thomas (Bruce Dern), while family (Selby's) is distant and estranged, or well-meaning but uncomprehending. For this is an America of night and neon, rootless drifting dreamers, cinderblock bus terminals and automobiles, where the sex act takes place on four rubber wheels and people fall in love on eight wooden ones at roller rinks.

The muted pop score seems well-chosen, not mere easy period setting -- Tommy James and the Shondells' 1969 quasi-psychedelic "Crimson and Clover" perfectly placed -- so that no subliminal tricks create automatic response, not even Theron's voiced-over memories. Attention is rigidly on the nearly always on-screen Aileen, whose simple-complex personality fascinates like a venomous serpent.

No, one cannot empathize, even while held by a superb performance and an unpleasant tale told well. Neither Jenkins' "most hopeful person I've ever encountered," nor Broomfield's "most honest person," Wournos stalks the imagination. 

(Released by Newmarket Film Group and "R" for strong violence, sexual content and for pervasive language.)