It was a tragic end to what may have been years of domestic abuse, stretching from one generation to the next.

A 31-year-old optician in the US apparently shot dead her father, brother-in-law and his father, before turning the gun on herself, all in one afternoon.

In between, she put up a furious Facebook post about why she did it.

On Tuesday (Aug 23) police rushed to a home in a quiet neighbourhood in the town of Lynn, Massachusetts, after getting reports of gunfire, and found two men dead.

A third man was found dead in a minivan outside another residence, and the young woman’s body was in her car in a supermarket carpark.

The names of those who died were not officially released immediately but multiple media reports identified them as Mohamad Sharifi, 66; his son-in-law Sanjar Halin, 34; and the latter’s father, Abdul Halin, 56.

The killer was identified as Khosay Sharifi, who said in her post, apparently written in her car just before she shot herself, that her twin sister had endured physical and emotional abuse by her husband for 14 years, and neither their family nor his would do anything about it.

She said her father had been just as abusive of their mother, and she did not want her two nieces to grow up seeing that any more.

Her brother-in-law “choked, slapped, kicked and swore” at her sister before he “punched her in her face”.

The post said: “My parents & his parents knew all these years but have not really done much but say ‘work it out’, ‘what will people say if you separate’ or even victim blaming.

“I'm trying to say all this as nice as I can so my post doesn't get deleted. There's no excuse for what he did.

“He kept doing it because no one did anything about it. How long did he think he would get away with it?”

Khosay also spoke directly to her sister, writing: “I hope you start healing & actually teach your daughters that abuse is not ok as they have also witnessed him slap you.

“I asked how they felt about that & they said they were scared & didn't know what to do. Let's not pass this on to your kids as it has been passed on to you.

“My father has also been abusive before & verbally but mostly financially abusive to my mum from what I've personally witnessed.

“Maybe that's why my mum did not protect her own daughter, because she's a victim too. But that's no excuse, how can you let your own daughter get abused.”

Those who knew the family were shocked. A friend told DailyMail.com that it was “not in (Khosay's) nature to be a killer” and she was “not a horrible person”.

But the sisters had a “rough upbringing”, with the parents having a lot of control over their life.

Friends did not seem to know about the abusive marriage.

But one of them was quoted as saying: “Her sister had it the worst, she had her hands full. Her husband didn’t seem too helpful. She wore a lot of hats. The cook, the maid, the nanny, the driver. She did everything.”

Khosay ended her post by saying that she wouldn’t suffer life with the wrong person.

“Don't force me to be with the wrong person just for the sake of marriage,” she wrote.

“This whole mindset of ‘just work it out’ needs to change because it is not healthy. I will not deal with this nonsense.”

Surviving members of the family started a crowd-funding campaign for help to hold the funerals, made a reference to mental health, and said they were heartbroken.