Aaron Brown was a bouncy, healthy infant until, when he was 10 weeks old and crying, his father­ shook him so violently­ that he was left permanently brain damaged.

But as the prosecutor in the case told me in 1998: “This mother just would not let this child die.’’ Elsa Lashley, who had shared a Brockton apartment with her husband and baby, had Aaron baptized in the intensive care unit at Children’s Hospital, leaving his side only once: to take out a restraining order against her husband, Leroy Brown.

She divorced Brown and testified against him at trial. Brown was convicted of assault and battery on a child causing substantial injury. Though prosecutors had asked for the maximum sentence of nine to 15 years, a judge gave him only three years.

At the time, Michael J. Sullivan, then the Plymouth district attorney, noted: “But for the grace of God, this would have been a murder case, not an assault and battery.’’

Lashley refused to accept Aaron’s limitations and has always seen him as a precious gift. A week ago, she threw a big party for his 21st birthday at a banquet hall in Avon. There was Aaron, in his wheelchair, wearing a Red Sox hat, and next to him was his mother. It’s harder to say whose smile was bigger.

Aaron can’t walk or talk and is legally blind. He eats through a feeding tube and remains in a diaper. He has seizures. He’s on a ketogenic diet used to control epilepsy.

Each night, Lashley gets up several times to get him a cup of water, to catheterize him, and to turn him over. Before dawn, she mixes his formula with nutrients, puts it in his feeding tube, and gets him dressed for school. After school, she gives him his medicine, then a shower, changes his clothes and brushes his teeth. His last tube feeding is at 9:30 p.m.

When Aaron graduated from a special program at Brockton High School in the spring, she got him a cap and gown and bought a class ring. “He looked really good,’’ Lashley says. “The only thing he didn’t do was go to the prom.’’

In 2007, Lashley met a nice guy and remarried. She and Phillip Charles have a daughter, Elyssa, who recently turned 7. She’s on the autism spectrum, and the family of four had waited years for a larger handicapped-accessible apartment from the Brockton Housing Authority, since Aaron and Elyssa had to share a bedroom and were constantly waking one another.

A Globe reader who befriended Lashley after I first wrote about her years ago said enough, already. She bought a three-bedroom home in Brockton, which Lashley picked out, and is renting it to the family. She, and Lashley, are my heroes.

“It’s a great house, and we are so happy,’’ Lashley says. “We’ve got a yard and a garden and we’ve planted squash and strawberries. Aaron and Elyssa have their own bedrooms.’’

There’s a ceiling-mount lift over Aaron’s bed, with funds donated by the Matty Eappen Foundation so Lashley can move him from bed to wheelchair and back.

In a 1997 case that made headlines worldwide, Matthew’s British nanny, Louise Woodward, was convicted of second-degree murder in the shaking death of the 9-month-old baby. Woodward was facing life in prison when Judge Hiller Zobel reduced the conviction to involuntary manslaughter and sentenced her to time served since her arrest, 279 days.

One of the prosecution’s key witnesses was Dr. Eli Newberger, who in 1970 founded the child abuse unit at Children’s Hospital. Newberger, who examined baby Matty when he was brought to the hospital, testified that he was the victim of violent prolonged shaking, and that a blood clot on his brain and a fractured skull indicated he had also been slammed against a hard surface.

The case still frustrates Newberger, as do the growing legal challenges to shaken baby syndrome. In June, the state Supreme Judicial Court ordered a new trial for a man convicted of severely injuring his baby daughter, after a Middlesex jury had convicted him of violently shaking her.

And Middlesex District Attorney Marian Ryan’s office previously dropped murder charges in two other cases after the state medical examiner’s office said it could no longer stand by its findings that the deaths were the result of shaken baby syndrome.

Such findings infuriate Newberger. “Starting with the Louise Woodward murder case, where her lawyers were permitted to spin their spurious theory every day after trial, a cadre of well-paid ‘experts’ have sold their opinions to a well-funded defense and a credulous public, through media that relishes conflict and pseudoscience,’’ Newberger says.

In a July 2016 article, the Journal of Pediatrics surveyed physicians at 10 leading children’s hospitals who deal with injured babies. The vast majority of the doctors agreed that shaken baby syndrome and abusive head trauma are valid medical diagnoses and that none of the alternative theories, except motor vehicle collisions, could result in such traumatic injuries in babies.

Elsa Lashley has never been to medical school. But she’s an expert on shaken baby syndrome.

“It’s real,’’ she says, simply. “I’ve seen it close up. Thank God Aaron survived, and he’s still here today.’’

Bella English writes from Milton. She can be reached at english@globe.com.