PARKLAND, Fla. >> Nikolas Cruz was immature, quirky and depressed when James and Kimberly Snead took him into their Parkland home. But he was pleasant and seemed to be growing happier, they said.

How the 19-year-old turned into a killer still baffles them.

“We had this monster living under our roof and we didn’t know,” Kimberly Snead told the South Florida Sun Sentinel in an exclusive interview today. “We didn’t see this side of him.”

“Everything everybody seems to know, we didn’t know,” James Snead said. “It’s as simple as that.”

Cruz still lived with the Sneads on Wednesday when he walked into Marjory Stoneman Douglas High School with an AR-15 rifle and killed 17 people — the worst school shooting since Sandy Hook.

The Sneads’ son had asked whether his friend could move into their home last Thanksgiving. Cruz’s mother, who had adopted him, died of pneumonia Nov. 1, leaving him without parents. He stayed briefly with a family friend in the Lantana area but wanted to move on.

The Sneads quickly agreed — though they realized he was extremely depressed about his mother’s death.

Five days before the shooting, Kimberly Snead took Cruz to the office of a therapist she has been seeing to deal with her grief over her dad’s death. Cruz said he was open to therapy but didn’t like medication. He took a business card and was figuring out what his health insurance would cover.

James, 48, is a decorated army veteran and a military intelligence analyst who served stints in the Middle East between 1988 and 1996. Kimberly, 49, is a neonatal intensive care nurse who cares for premature and ill babies.

They told Cruz there would be strict rules in their home.

“I told him there’d be rules and he followed every rule to the T,” James said.

The couple both grew up around guns and are comfortable with them, but they insist on gun safety.

They made Cruz buy a locking gun safe to put in his room the day he moved in. Cruz had a handful of guns, including the AR-15 and two other rifles that Snead said would be considered assault rifles. Cruz, a hunter, also had knives, BB guns and pellet guns.

Snead thought he had the only key to the cabinet but has figured out Cruz must have kept a key for himself. The family kept their own rifles, bought after a burglary a couple of years ago, in a separate locked cabinet.

They told Cruz he needed to ask permission to take out the guns. He had asked only twice since November. They said “yes” once and “no” once.

Cruz’s mom seemed to have cosseted him.

“He was very naive. He wasn’t dumb, just naive,” James said.

He didn’t know how to cook. They had to show him how to use a microwave. He didn’t know how to do his laundry and also had to learn to pick up after himself.

He didn’t drive but bought a bicycle and rode it to work at a nearby Dollar Tree.

The Sneads had raised their own three boys and jokingly called the process of teaching Cruz “Adulting 101.”

They insisted he enlist in adult education classes run by the school district and drove him to school each day. He didn’t have much time to himself.

He seemed to be doing well and wanted to be an army infantryman. He was excited when an army recruiter visited school recently.

So far as they know, Cruz wasn’t particularly close to any of the victims and they don’t know of any resentment he might have had against any of the people who were murdered. They have no clue why he did it.

The night before the massacre seemed just like any other, they said.

Cruz had some odd eating habits. He quietly put a chocolate chip cookie in his steak and cheese sandwich. He went to bed around 8 p.m., which wasn’t unusual.

They said they were sure he was bullied; he was the kind of kid that would attract the attention of a bully.

He badly wanted to have a girlfriend and seemed lonely, they said. They don’t know anything about rumors they’ve since heard about a breakup with a girl, stalking or fighting.

They also saw no signs of animal cruelty. They are animal lovers, with two dogs and six cats. He’d have been kicked out if he was mean to their animals. Cruz seemed to love their pets.

On Wednesday morning, Cruz told them he didn’t need a ride to school: “It’s Valentine’s Day and I don’t go to school on Valentine’s Day,” he said.

Cruz had a “boxer’s fracture” in his right hand after falling on a step in their house about three weeks ago. They now think he removed the cast on his hand, the second he’d had, the day of the shooting. He’d also removed the first cast.

Kimberly last saw him around 10 that morning before she left to run errands. He said he was going fishing and was gone when she returned. She went to sleep because she was supposed to work a night shift that night.

Cruz sent their son a few texts that day. In one, he asked what classroom the boy was in. He said he was going to see a movie.

Later he texted he had “something important” he wanted to tell the teen. Then he wrote: “Nothing man.”

They have since figured out those texts were sent during the Uber ride Cruz took to the murder scene. His last text to their son, as Cruz pulled up at the school, said “Yo.”

They think Cruz moved out of the home of his late mom’s friend in Lantana because of tension about his guns and a possible misunderstanding about money.

Cruz told them he stood to inherit at least $800,000 from his deceased parents. Most of the money would come when he turned 22, he said. The Sneads have since seen paperwork they think supports the claim he was going to be very financially comfortable.

Cruz thought the family friend in Lantana was stealing money from him but the Sneads suspect she was innocent and he was just a victim of common identity theft. They reported about $2,900 in fraudulent charges on his debit or credit card.

Around 2:30 p.m. Wednesday, their son called sounding panic-stricken. He was safe but had heard shots fired on campus. He helped classmates flee by climbing a fence to neighboring Westglades middle school.

Snead told his son to walk to Wal-Mart and he’d come get him.

As Snead drove there, a SWAT commander called his cellphone and asked where his son Nik was. Told him it wasn’t his son and he didn’t know where he was.

As he kept driving and put two and two together, he became terrified and called the commander back. Snead told the cop the last he knew Nik was home alone with Kimberly: “I need a police presence at my house. Go make sure my wife is OK.”

Snead called his son to say he needed to check on mom first and drove home: “I was fearing for her life.”

Kimberly was sleeping because she was supposed to work the night shift that night. Law enforcement banged on her door with guns drawn, yelling: “Put your hands up.”

When they asked where her son was, she assumed something terrible had happened to her son but soon realized they meant Cruz. They searched the house but already had Cruz in custody elsewhere.

After an emotional reunion of husband and wife, they were brought to Broward Sheriff’s headquarters to be reunited with their son. They later realized he was being questioned by detectives in case he was involved. Investigators quickly figured out he was innocent.

As they waited, Cruz was led in to the building, handcuffed and wearing a hospital gown, surrounded by deputies.

Kimberly tried to run at him, James held her back.

“Really, Nik? Really?” she yelled at him.

“He said he was sorry. He apologized. He looked lost, absolutely lost,” said James. “And that was the last time we saw him.”