This photo provided by the Broward County Jail shows Nikolas Cruz. Authorities say Cruz, a former student opened fire at Marjory Stoneman Douglas High School in Parkland, Florida, killing 17 people. Picture: Broward County Jail via AP

Parkland -- The killing began with the squirrels. As a fourth-grader, Nikolas Cruz would try to bloody them with his pellet gun. Then he started going after chickens.

By the time Cruz was a teenager, he was sneaking into his neighbours' yard across the street and trying to get his dogs to kill their baby potbelly pigs.

One resident watched him take long sticks to rabbit holes, ramming them down as hard as possible to kill any creatures trapped inside.

Some in the affluent neighborhood where Cruz grew up said they called authorities on him frequently. Every few weeks, it seemed, police cruisers were pulling up to the teenager's house to sort out the latest complaint.

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In recent years, the behaviour got worse. Cruz became more isolated, sitting on his own at the school bus stop, sneering at neighbours, withdrawing even from his younger brother, friends and classmates said.

Some who knew Cruz cut ties in part because of his unnerving and scary Instagram posts and photographs, including one showing a gun's laser sight pointed at a neighborhood street. Another appeared to show a dead frog's bloodied body.

Others saw a teenager trying to work through a dark period of his life and tried to help. In short order, Cruz was expelled from school, lost his mother to pneumonia and slunk into a depression.

A friend from his former high school took him in. His parents gave Cruz their guest bedroom, got him a job and drove him to an alternative school every day to work on his GED.

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But no one - not those who feared him nor those who sympathised - glimpsed the full malevolence brewing inside Cruz's heart until Valentine's Day, when police say he walked into a suburban south Florida high school and carried out one of the nation's deadliest school shootings.

Cruz was adopted at age 2 along with his 2-month-old brother, Zachary, by Lynda and Roger Cruz, friends and relatives said. Relatives said Nikolas and Zachary shared a biological mother but have different fathers.

Their adoptive father died of a heart attack when they were young, leaving Lynda to raise the two boys on her own.

"Lynda was very close to them," said her sister-in-law, Barbara Kumbatovic. "She put a lot of time and effort into those boys, trying to give them a good life and upbringing."

Zachary often seemed quiet and content to follow Nikolas' lead. But Nikolas was moody, prone to an explosive temper and at times seemed to delight in antagonising others.

"People were afraid of him," said Brody Speno, 19, who grew up on the same block.

"Just about everybody on this part of the street had a run-in with him," said longtime neighbour Malcolm Roxburgh, who lived just three houses down.

His hostility stuck out in this calm, well-to-do neighborhood of manicured lawns and sprawling tony homes.

Cruz picked fights with other kids. He stole people's mail. He threw rocks and coconuts and vandalised property, neighbours said. He lurked at late hours along drainage ditches running along the back yards of their houses. One woman said she caught him peeking into her bedroom window. Another caught him stealing their bike.

"Lynda dealt with it like most parents did. She was probably too good to him," said Kumbatovic. "She made a beautiful home for them. She put a lot of effort and time into their schooling, their recreation, whatever they needed. . . . She went over and above, because she needed to compensate for being a single parent."

A classmate through elementary and middle school, Brody Speno waited every day with Cruz to catch the bus to school. Then one afternoon about five years ago, when they both were teenagers, Cruz started throwing eggs at Speno's car with no warning, Speno recalled. He and a friend chased Cruz back to his house.

"We were pissed off, so we knocked on the door and his mom came out," Speno said. When the two told her what happened, Cruz's mom had a strange reaction.

"She said, 'No, my son would never do that. He's inside sleeping,' " Speno recalled.

There were visible indications of troubles in their home. Three neighbors recalled seeingfurnitureon the curb to be hauled away every few months. The hutches and tables often looked like they had been kicked in or smashed up by someone.

For years, Roxburgh's daughter Rhonda drove past Cruz in the morning as he waited for the school bus. One morning about four years ago, Rhonda Roxburgh said, Cruz suddenly attacked her car, slamming it hard with his backpack.

When she got out to confront him, Cruz simply laughed and sneered, so Roxburgh called the police. For the next few mornings, Rhonda Roxburgh said, police stationed an officer at the intersection to make sure Cruz didn't attack or throw rocks at cars.

Fed up with the terrorising, Roxburgh said she confronted Cruz's mother, but again, she refused to believe her son had done it.

While Roxburgh was talking to Lynda Cruz, however, she saw the boy sneaking out of the house. So she went to confront him, too.

Roxburgh said she told the teenager, "Look at me when I'm talking to you."

When Cruz did, the look he gave chilled Roxburgh to the core.

"It was just so cold. Like empty, cavernous eyes," she said. "No feeling at all."

At school, classmates had similar reactions.

The signs were minor at first, said Dakota Mutchler, 17, who attended middle school with Cruz. But as Cruz transitioned into high school, he "started progressively getting a little more weird."

Cruz started selling knives out of a lunchbox, Mutchler said, posting on Instagram about guns and killing animals, and eventually "going after one of my friends, threatening her."

In a school where cliques were common, Cruz never seemed to find his crowd.

Mutchler recalled Cruz getting suspended from school repeatedly, before he was expelled last school year.

A classmate, Victoria Olvera, 17, told the Associated Press that Cruz was expelled after a fight with his ex-girlfriend's new boyfriend.

In a phone interview, another classmate, Jevon Cange, 21, said he saw Cruz headed to the administrator's office one day in 2016. Cruz told him he had been in a fight. By the next time Cange saw him in late 2016, Cruz said he had been expelled.

"When someone is expelled, you don't really expect them to come back," Mutchler said. "But, of course, he came back."

Math teacher Jim Gard, who taught Cruz last school year before he was expelled, said that the school administration sent out an email to teachers with a vague suggestion of concern, asking teachers to keep an eye on him.

"I don't recall the exact message," Gard said, "but it was an email notice they sent out."

Broward County Mayor Beam Furr told CNN that Cruz had been receiving treatment at a mental health clinic for a while, but that he had not been to the clinic for more than a year.

The hardest blow came in November, when Cruz's mother died of pneumonia at 68, relatives said. With her death, Cruz lost one of the only people close to him, said friends and family.

For a while, Cruz and his brother stayed with friends in Latana, in Palm Beach County, Fla. The situation deteriorated, and Cruz asked a former classmate from Marjory Stoneman Doulgas High School whether he could move in with his family, said Jim Lewis, a lawyer representing the family.

"The family brought him into their home," Lewis said. "They got him a job at a local dollar store. They didn't see anything that would suggest any violence. He was depressed, maybe a little quirky. But they never saw anything violent."

The family knew Cruz had been in some fights and had the impression Cruz had been bullied, Lewis said.

"This family was just trying to do the right thing by this kid, because they felt sorry for him," Lewis said. "Now they've found themselves in his horrible position where they are second-guessing everything."

To the family, Cruz mostly seemed depressed.

"Who's not going to be depressed?" Lewis said. "You're 19 years old. Your father's been dead 12 years. The mother's the one who raised you and all that you've basically got in the world in terms of grounding you. And all of sudden she dies of pneumonia."

Moving in to his friend's house, Cruz brought with him the AR-15 gun police say he would later use to gun down his classmates and teachers. The family let him keep it in a locked steel safe in his room. They never saw him shoot it, Lewis said.

He was respectful, followed the rules and seemed grateful to have a home. Up until the shooting, there was no sign of trouble.

Just the day before, he had ridden with his friend's father to the alternative school where he was working on his GED, then went to his job at the dollar store.

Then on Wednesday, Cruz said he wasn't going to school.

"It's Valentine's Day. I don't go to school on Valentine's Day," he told them, according to Lewis.

That morning, the family's son, however, went as usual to Dougals High, where he is a junior. When the shooting began, the son was in class, and remained locked in the room until police let him and others out.

"He was in class and ran out with his hands up like everybody else," Lewis said. He had no idea that Cruz was allegedly the one killing classmates until the investigators asked him to come with them to the police department.

That, Lewis said, was the first indication they had of the depth of violence inside Nikolas Cruz.

The Washington Post