MIAMI (NYTIMES) - The man who shot and killed a toddler and the child's grandmother at a Publix grocery store in Palm Beach County, Florida, last week had no relationship with the victims and, according to the authorities, had written on social media that he wanted to "kill people and children".

The gunman, identified by the Palm Beach County Sheriff's Office as Timothy J. Wall, 55, of Loxahatchee, Florida, shot and killed himself in the store in Royal Palm Beach, Florida, last Thursday morning (June 10) after fatally shooting the woman and her grandson, the authorities said.

The Palm Beach County sheriff, Mr Ric Bradshaw, said the shooting might have been prevented if someone had warned his department about Mr Wall's dangerous Facebook posts.

"If somebody would've let us know who he is, we would have contacted him, see if he's got a gun, get him into mental health, and you wouldn't have two people dead," Mr Bradshaw said at a news conference last Friday.

But former relatives of Mr Wall said they had tried to warn the authorities about him. His former sister-in-law, Ms Maia Knight, told The Palm Beach Post that her sister, Mr Wall's ex-wife, had contacted local officials about him. Ms Knight also said that Mr Wall had schizophrenia.

"My sister was going to the courthouse, going to police, telling everyone he needs help," Ms Knight told The Palm Beach Post. "My sister was trying to help him but didn't know how."

Ms Knight and Mr Wall's ex-wife Monica Sandra Wall did not respond to requests for comment.

The names of the victims - the woman, who was 69, and her grandson, who the authorities said would have turned two this month - have not been released. The authorities said their family has invoked a 2018 amendment to Florida's Constitution that allows crime victims and their relatives to keep their identities private.

At the news conference last Friday, Mr Bradshaw emphasised that the shooting was just the latest one carried out by a man who had posted disturbing statements online and who suffered from clear "mental unstableness".

"This tragedy fits the profile across the United States when these things happen," the sheriff said.

The authorities are inundated with reports of potentially dangerous people, making it a challenge for them to identify who is actually a threat, said Professor Jonathan Metzl, the director of the department of medicine, health and society at Vanderbilt University.

Families have the burden of proving that the person they are warning the authorities about is worth monitoring. That may be why law enforcement officials did not notice someone like Mr Wall, Prof Metzl said.

"Of course they're going to blame it on the family because otherwise it would be their fault for not doing something," Prof Metzl said.

A Palm Beach County sheriff's spokesman, Ms Teri Barbera, said on Monday that Ms Monica Wall made one report to the Sheriff's Office about Mr Timothy Wall, in May 2019. According to the incident report, Ms Monica Wall said that Mr Timothy Wall was an alcoholic, owned a gun and had not worked in two years.

Even though Ms Monica Wall had filed for divorce in 2017, Mr Timothy Wall had not found a place to live and was still sharing a home with his former wife, according to the report.

Sheriff's deputies told Ms Monica Wall at the time that if she feared for her safety, she should "stay with friends" until she could evict Mr Timothy Wall.

He was evicted from the home the couple shared in West Palm Beach later in 2019, court records show. Mr Timothy Wall filed for bankruptcy protection in January.

Mr Timothy Wall filed a complaint of his own against Ms Monica Wall in June 2019, saying that Ms Monica Wall picked up their daughter at school and "ran away" with the child.

Ms Monica Wall's lawyer told deputies that Mr Timothy Wall had no parental rights over their daughter, the report said.

On Thursday morning, Mr Timothy Wall walked into the Publix store in Royal Palm Beach, about 12 miles (19km) west of Palm Beach, holding a golf putter that he appeared to be using as a walking stick, the authorities said.

He had walked into the store earlier that morning, the Sheriff's Office said, but video surveillance footage showed him leaving after he spotted a sheriff's deputy.

He walked inside again at 11.29am and saw the grandmother and the child near the produce section, the Sheriff's Office said.

As the grandmother scanned the produce section, Mr Timothy Wall looked at her and then began to walk towards her, the Sheriff's Office said.

Mr Timothy Wall fired one round at the child, killing him, the sheriff's office said.

Ms Barbera said Mr Timothy Wall used a Springfield XD-M .45-caliber pistol, but he was not the original purchaser of the gun. Investigators are still trying to determine how Mr Timothy Wall obtained the gun, as well as its origins, Ms Barbera said.

The grandmother then tried to stop Mr Timothy Wall, the Sheriff's Office said. The struggle between Mr Wall and the grandmother "may have caused the gun to malfunction", leading Mr Wall to reload, Ms Barbera said.

"It is believed the grandmother may have helped prevent an even worse tragedy from occurring," Ms Barbera said in a statement.

As Mr Wall and the grandmother struggled, he pushed her to the ground and shot her, the Sheriff's Office said. Mr Wall then shot and killed himself.

"The real sad part of this, other than the fact that two people are dead, is that there was a chance this could be stopped," Mr Bradshaw said, citing Florida's "red flag" gun law, which allows judges to seize guns from potentially dangerous people.

The law was passed in Florida after the shooting at Marjory Stoneman Douglas High School in Parkland in 2018, which left 17 people dead.