Lee Harvey Oswald may or may not have been an assassin, but his mother certainly was a killer.

All right, Marguerite Oswald didn’t literally murder anyone. But when you have three sons and none of them welcome your company, you’ve managed to snuff out something inside them.

What we see in Rob Urbinati’s MAMA’S BOY – the riveting drama at the George Street Playhouse in New Brunswick, New Jersey — is that Mrs. Oswald had no idea of what a monster she was.

And there’s no worse type of monster than that.

We meet her at New York’s Town Hall on February 18, 1964 – fewer than 100 days after President John F. Kennedy had been assassinated in Dallas. She’s about to address a capacity crowd, and that she comes on as a superstar immediately tells us reams about her.

“You shall know the truth,” she snarls in no uncertain terms. “Lee was tried and convicted in a few hours but he was not guilty. He had a different role. I will tell you who killed the president.”

Well, that’s quite a grabber. We’ll all stick around for that, because we’re all so hungry for any explanation of one of the world’s greatest mysteries.

John Weidman in ASSASSINS, the 1990 musical he wrote with Stephen Sondheim, stated that “Fifty years from now, they’ll still be arguing about the grassy knoll, the Mafia, some Cuban crouched behind a stockade fence.” Actually, Weidman underestimated, for we’re now at 53 years — and counting.

There’s another reason to stay seated: Betsy Aidem is giving one of the season’s finest performances as Marguerite. Aidem seems to be THE GLASS MENAGERIE’S Amanda Wingfield on the speediest speed. She’ll maintain that fervor when the action flashes back to a few years earlier: Marguerite and her son Robert are visiting newlyweds Lee and Marina, just home from the Soviet Union, from where Lee recently defected only a few years after he’d abandoned America.

Here Aidem perfectly captures the attitude that some mothers have: because she gave birth and is older, she’s therefore automatically infallible. Marguerite believes she has all the answers — and she’ll give them even when her two sons aren’t asking her any questions.

“But,” you’re saying “you mentioned three sons.” Yes, but John is never seen, and not just because Urbinati wanted to save a theater a salary. John left town long ago and wouldn’t even tell his mother where he went. Both brothers who’ve stayed on the scene fully understand why.

Marguerite clearly favors Lee, so Robert works hard to win her love. But he nevertheless flat-out tells her when he thinks she’s wrong – which he often does because she often is.

That doesn’t matter to Marguerite. Aidem shows us this woman’s metaphorical suit of armor that’s makes the outfits that medieval knights wore tin foil in comparison. Insult her if you will – and all three characters constantly do — and she’ll simply choose not to hear any affront but will move on to her next issue. Her eyeglasses may help her vision, but she’s mentally myopic.

We infer that Lee married a foreigner and brought her to his turf so he’d finally be able to dominate a woman, which he’s never been able to do with his mother. Marguerite wants Lee and Marina to live with her now and forever, but when he decides that they must move out of her house, his courage only goes so far. What he does at this moment is particularly telling.

What else can be expected from a son who was made to sleep in the same bed with his mother until he was 12 – because, Marguerite claims, their small apartment demanded it? Note that Lee calls his wife “Mama.” That she’s given birth to their child would be his official excuse if he were questioned about it, but we know there’s more to it.

In GYPSY, Rose is a true smother-mother, but at least she eventually acknowledges that “Mama’s got to let go.” Marguerite doesn’t believe she should and even implies that if Lee doesn’t stay, she’ll tell his new boss about his dishonorable discharge. Aidem shows that Marguerite fully believes that she’s playing fair with him.

Yeah, she’s a mother, all right. And just when you think she can’t possibly get any worse, she finds out where they’ve moved and shows up. She feels she can buy their love by giving presents and expecting that she’s now entitled to inclusion and respect.

Marguerite doesn’t just admit but blatantly tells the couple that she’s been literally been stalking their house for hours at a time to see when they’re coming and going. “Him and his big secrets!” she says of Lee – reminding us that he might well have plenty of them that she can’t even imagine.

But Urbinati is careful to humanize Lee, whom actor Michael Goldsmith does resemble and brings to vivid life. That we first see him in a suit and tie is effective, because the few pictures we know of Lee Harvey Oswald have never shown him in lofty clothes. Urbinati also lets us see that Lee was a doting dad and said “I like Kennedy” – albeit early in the play.

However, Lee doesn’t like his life. “I have a dirty job with shit pay,” he says of his $50 a week welding stint. “And the government thinks that any defector who comes back is a spy.” Can we really blame the powers-that-be for that assumption?

Whether or not Goldsmith and Laura Casillo, who plays Marina, are actually fluent in Russian, they certainly seem to be. Casillo artfully shows the trajectory of how the shrinking Soviet violet in Act One can bloom into an All-American consumer by Act Two. As Robert, Miles G. Jackson’s wonderfully unmannered performance shows the anguish of a less-loved child. He and Casillo are adept at displaying their feelings of responsibility in Lee’s failures prior to their sharing a surprising scene.

“Lee may have his bad points,” Marguerite insists. “But so do all of us.”

So even after Lee is jailed, she simply and steadfastly believes he’s innocent and will soon be freed. But it’s the statement she makes to Robert and Marina a bit later that got the biggest “Oooooh!” from the audience in a play that spurs plenty of them. Watch for it.

David Saint has staged the play in fine fashion, but his best moment comes when he places Marguerite downstage far left and Lee upstage far right – prior to having her lovingly say “Come to mama.” The will-he-or-won’t-suspense is powerful.

As the strongest scene, however, let’s nominate the one in which Marguerite, Marina and Robert are watching TV that Sunday morning after the assassination and are waiting for Lee to walk through the gauntlet of reporters. Has there ever been a more powerful example of dramatic irony – where we know what’s going to happen and the characters on stage don’t?

And yet, the play’s most chilling line is Robert’s statement to Lee during the homecoming celebration: “You can’t change the world, kid.”

But that’s precisely what Lee Harvey Oswald did — unless Marguerite Oswald manages to convince you otherwise.