FILE - In this May 14, 2013, file photo, O.J. Simpson appears at an evidentiary hearing in Clark County District Court in Las Vegas. In a letter that surfaced after her 1994 death, Nicole Brown Simpson detailed the fear and violence that framed her marriage to O.J. Simpson. In the 25 years since then, spousal abuse has moved from a private matter to a public health concern. (Ethan Miller via AP, Pool, File)

In a letter that surfaced after her 1994 murder, Nicole Brown Simpson detailed the fear and violence that framed her marriage to O.J. Simpson, the charismatic football star who became a TV pitchman.

Simpson gave her "disgusted" looks with each pound she gained in her first pregnancy in 1988 and "beat the holy hell" out of her a year later, when the couple told an X-ray lab she fell off a bike, she wrote. Three years later, on June 12, 1994, she and friend Ron Goldman were fatally stabbed outside her Los Angeles condominium as her two young children with Simpson slept inside.

Simpson's murder trial the following year transfixed the nation and raised troubling questions about the intersection of race, celebrity and criminal justice. What's sometimes forgotten, a quarter-century later, is how the case also shifted the country's view of domestic violence from a largely private matter to a public health concern.

As the trial unfolded, calls to hotlines, shelters and police exploded.

"Her murder hurled into the forefront a conversation that advocates had been having for years — that it could happen anywhere, to anyone," American University professor Rachel Louise Snyder wrote in a new book titled "No Visible Bruises: What We Don't Know About Domestic Violence Can Kill Us."

In the years that followed, with funding from the 1994 Violence Against Women Act, policy-makers began seeking new ways to address domestic violence beyond sending battered women to shelters and giving them restraining orders that often did little to protect them.

Advocates now see the need for comprehensive services to help victims start over. And more prosecutors are pursuing cases that rely on forensics, medical records and other hard evidence, rather than a victim's testimony, to bring suspects to court. They try to assess the risk of homicide by weighing risk factors, including substance abuse, gun ownership, forced sex, children by other fathers, violence during pregnancy and stalking. Perhaps the biggest red flag of all is any instance in which an abuser tries to choke off a person's airway.

"Statistically, we know that once the hands are on the neck, the very next step is homicide," San Diego Detective Sylvia Vella tells Snyder in the book. "They don't go backward."

Efforts are also underway, often court-ordered, to try to counsel and rehabilitate batterers, who were once written off as incorrigible.

Nationwide, more than 1,100 women are killed each year by intimate partners, most often by gunfire, according to a 2018 report by the Violence Policy Center that used 2016 FBI data.

One in 4 women and 1 in 9 men are the victims of non-lethal domestic violence, which is defined as serious physical abuse, sexual abuse or stalking, according to the Centers for Disease Control and Prevention. Domestic violence hotlines receive 20,000 calls every day in the United States, according to the National Network to End Domestic Violence.

Simpson was acquitted of the double murders at his 1995 trial but found liable for the deaths at his civil trial, when Nicole Brown Simpson's undated letter to him was introduced. He said he had never seen it before her death.

Anyone reading it might wonder why she stayed with Simpson for so long and reconciled for a time after their 1992 divorce. It's a common question to ask, but the wrong one, Snyder believes. Many victims work on their exit for years.

"We do not recognize what leaving looks like, and how dangerous it is and how long it takes," Snyder said in an interview.

In her book, Snyder explores long-held myths about domestic violence through the lens of several women killed in the years after Nicole Brown Simpson. They were neither rich nor famous, but their experiences mirrored hers in many areas — their abusers were older and controlling and fathered children with them, and the women were often reluctant to seek criminal charges after reporting abuse to police.

The deaths of Michelle Monson Mosure in Billings, Montana, in 2001, and Dorothy Giunta-Cotter in Amesbury, Massachusetts, in 2002, led local agencies to conduct lengthy reviews.

Giunta-Cotter had hopscotched across New England seeking safety in shelters before deciding that she and her children couldn't hide from her husband forever. She moved back home to Amesbury, hoping that her children would at least escape if he came for her.

That exact scenario soon came to pass. Days after holding her hostage at the house, and being released on $500 bail, William Cotter killed his wife and then himself with a sawed-off shotgun, after blowing past their 11-year-old daughter at the door. Another daughter was at a friend's house.

Mosure was impregnated at 14 by her 24-year-old boyfriend and had a second child with him before finishing high school. When the youngest started school, she enrolled in nursing school, although she learned she had to marry Rocky Mosure to get financial aid not tied to her parents' income.

"For Michelle, it was the biggest irony of her life, a system that forced her to marry a man she was working so hard to leave," Snyder writes.

Not long after, Mosure shattered the window of the bolted back door at her mother's house, where she had dropped off their children. When his parents bailed him out of jail, an alarmed Michelle Mosure recanted her affidavit and moved back in with Mosure. Two months later, he killed her and the children in their basement before turning the gun on himself.

Authorities in both communities realized that shelters alone were not a solution, that danger peaked after an arrest and that abusers need to be jailed or monitored until victims can make a safety plan. They also concluded that guns increase the risk exponentially.

For many people in volatile relationships, child custody issues can be especially treacherous.

"You are tied to that person you have a child with for 18 years, even longer, honestly. For a lot of our clients, that is a very terrifying thing," said Stacy Dougherty, community outreach director at Laurel House, a domestic violence shelter in the Philadelphia suburbs, where two women were killed in recent months during custody exchanges at convenience stores.

After spending 10 years researching domestic violence for her book, the issue hit close to home for Snyder last week, when a couple she knew from her daughter's school community in Washington, D.C., died in a murder-suicide during a contentious divorce. Snyder, a friend of the extended family, said Jason Rieff was set to lose custody of their children while Lola Gulomova took them overseas on her next State Department assignment.

According to a police report cited by The Washington Post, Rieff shot himself in the head after police arrived Friday morning. They found Gulomova's body in another room.

Snyder, faced with the difficult task of telling her daughter about the deaths, has not had time to fully analyze it yet.

"All I know is that this underscores the importance of my book and my work, and that people get desperate when they feel there is no way out," she said Tuesday. "We've made progress in that we know more" about domestic violence. "But we've lost ground in that this is still happening in such numbers."

This undated photo provided by Bloomsburg Publishing shows author Rachel Louise Snyder, who wrote “No Visible Bruises: What We Don’t Know About Domestic Violence Can Kill Us.” Nicole Brown Simpson detailed the fear and violence that framed her marriage to charismatic football star and TV pitchman O.J. Simpson in a letter that surfaced after her 1994 death. “Her murder hurled into the forefront a conversation that advocates had been having for years, that it could happen anywhere, to anyone,” Snyder said. (Don Rutledge/Bloomsburg Publishing via AP)
FILE - In this Nov 25, 1993, file photo, O.J. Simpson stands with Nicole Brown Simpson while broadcasting on the sidelines during the Thanksgiving Day NFL football game in Irving, Texas. In a letter that surfaced after her 1994 murder, Nicole detailed the fear and violence that framed her marriage to charismatic football-star-turned-TV-pitchman O.J. Simpson. (AP Photo/Ron Heflin, File)