PARKLAND, Fla. (AP) — Students and neighbors describe the suspect in the deadly rampage at a Florida high school as a troubled teenager who threatened and harassed peers, talked about killing animals, posed with guns in disturbing photos on social media, and bragged about target practice in his backyard with a pellet gun.

Nikolas Cruz, 19, had been expelled from Marjory Stoneman Douglas High School for "disciplinary reasons," Broward County Sheriff Scott Israel said, but he insisted he didn't know the specifics. Math teacher Jim Gard told the Miami Herald that before Wednesday's fatal shooting of 17 people, Cruz may have been identified as a potential threat - Gard believes the school had sent out an email warning teachers that Cruz shouldn't be allowed on campus with a backpack.

"There were problems with him last year threatening students, and I guess he was asked to leave campus," Gard told the paper.

Student Victoria Olvera, 17, said Cruz had been abusive to his ex-girlfriend and that his expulsion was over a fight with her new boyfriend. He'd been attending another school in Broward County since the expulsion, school officials said.

Cruz was an orphan — his mother, Lynda Cruz died of pneumonia on Nov. 1 neighbors, friends and family members said, according to the Sun Sentinel. Cruz and her husband, who died of a heart attack several years ago, adopted Nikolas and his biological brother, Zachary, after the couple moved from Long Island in New York to Broward County.

The boys were left in the care of a family friend after their mother died, family member Barbara Kumbatovich, of Long Island, said.

Unhappy there, Nikolas Cruz asked to move in with a friend's family in northwest Broward. The family agreed, and Cruz moved in around Thanksgiving. According to the family's lawyer, who did not identify them, they knew that Cruz owned the AR-15 but made him keep it locked up in a cabinet. He did have the key, however.

Jim Lewis said the family is devastated and didn't see this coming. They are cooperating with authorities, he said.

Longtime Cruz family neighbors Malcolm and Christine Roxburgh told the Sun Sentinel that the police came to the boy's house many times, as he used to get in trouble and harass people. Malcolm Roxburgh said a neighbor across the street kept pigs, and Nicolas Cruz targeted the family.

"He didn't like the pigs and didn't like the neighbors, so he sent over his dog over there to try to attack them," Roxburgh said.

His wife said she once caught Nikolas peeking in her window.

"I said, 'What are you doing here?' He said he was looking for golf balls. I said, 'This isn't the golf course,'" she said.

And, the couple said, when the boy didn't want to go to school, he would bang his head against a cement wall. They were scared of him. "He could have killed any of us," Christine Roxburgh said.

Cruz was getting treatment at a mental health clinic for a while, but hadn't been there for more than a year, Broward County Mayor Beam Furr said during an interview with CNN.

"It wasn't like there wasn't concern for him," Furr said. "We try to keep our eyes out on those kids who aren't connected ... Most teachers try to steer them toward some kind of connections. ... In this case, we didn't find a way to connect with this kid."

Officials said they're dissecting the suspect's disturbing social media posts, without elaboration. But peers said they recognized Cruz from an Instagram photo posing with a gun in front of his face. The students called Cruz "weird" and a "loner" - even those who'd been friendly with him said they hadn't seen him in more than a year since his expulsion.

Dakota Mutchler, 17, recalled Cruz posting on Instagram about killing animals and said he had talked about doing target practice in his backyard with a pellet gun.

"He started going after one of my friends, threatening her, and I cut him off from there," Mutchler said.

He said students weren't surprised officials had identified Cruz as the shooter: "I think everyone had in their minds if anybody was going to do it, it was going to be him." Mutchler said.

But Broward County School District Superintendent Robert Runcie said he did not know of any threats posed by Cruz to the school.

"Typically you see in these situations that there potentially could have been signs out there," Runcie said. "I would be speculating at this point if there were, but we didn't have any warnings. There weren't any phone calls or threats that we know of that were made."