(CNN) -- John Lajeunesse said he was heading to the Renegade Mountain area to go four-wheeling, nothing out of the ordinary for a 16-year-old kid in rural Tennessee.
How he and three other young people ended up shot dead inside a car on that same mountain is now a mystery before police and the small community of nearby Crossville.
A passerby discovered the car with the four victims, including a young mother, parked along a country road near the Renegade Mountain community Thursday morning.
Lajeunesse and a pair of 17-year-olds, Steven Presley and Dominic Davis, were the passengers. Rikki Jacobsen, a 22-year-old mother of a young boy, was in the driver's seat.
Three of the victims were current or former students of the local school district.
"It's something that reverberates through the entire community," said Donald Andrews, Cumberland County's school superintendent. "The loss of life is always tough, and especially (so) when it's young people."
Only one man has been publicly linked to the killings: Jacob Allen Bennett. Authorities said he was identified fairly quickly into the investigation and taken into custody around midnight Thursday without incident on a parole violation in nearby Rhea County.
Randy York, the district attorney general whose territory includes the crime scene, told reporters Friday that his office intends "in the very near future" to empanel a grand jury to consider charges against Bennett related to the four killings.
"The citizens of Cumberland County and Crossville can rest assured that we have the person who committed the crimes in custody, that the community is safe," said Tennessee Bureau of Investigation Director Mark Gwyn.
The 26-year-old Bennett had been booked in Cumberland County five times before this, in addition to arrests in other counties and another state, said Sheriff Butch Burgess. He did not detail any of Bennett's alleged crimes, beyond the fact he'd been charged in 2009, convicted, sentenced to prison, then released on parole.
If law enforcement authorities know more, they kept the facts close to the vest Friday -- including about how the killings were carried out and why. They have been working diligently since first learning of the deaths at 7 a.m. Thursday.
"They're kind of like robots, they're still going," said Burgess of the state and local investigators. "To them, it's not a job, especially when they see the circumstances involve kids. It hits home."
And then there are the victims' families, struggling to make sense of the bloodshed in a place where -- as many insisted -- these kinds of things just don't happen.
Michael Rick, who lives with Lajeunesse's family, said he dropped the 16-year-old at Presley's house on Wednesday afternoon.
Lajeunesse mentioned that the pair were going to go four-wheeling at around Renegade Mountain and spend the night at his friend's house.
The next day, Lajeunesse didn't call Rick to be picked up.
"You just get that gut feeling when nothing is right," Rick said.
It wasn't until Thursday night that police were able to confirm what they feared: Lajeunesse was among those killed.
According to the Cumberland County Board of Education, Lajeunesse had attended two local high schools, though most recently he's been home-schooled.
Davis was a sophomore at Cumberland County High School, having recently moved with his family to Tennessee from Colorado, said Andrews. Another victim, Presley, graduated from The Phoenix School in May.
As to Jacobsen, she had a son who attended a Cumberland County elementary school -- and whom she "loved more than life itself," according to a friend who asked not to be named before they had not been friends for long.
"She was very nice, she was innocent, and she couldn't stop talking," the friend said.
Located about 70 miles west of Knoxville and 110 miles east of Nashville, Crossville is a small city that serves as the county seat for Cumberland and its 57,000 people. It's a place that the school superintendent describes as a "down-home type community" where "everyone seems to know everyone."
As a result, everyone has been shaken by this week's carnage.
Students in the county's 12 schools, particularly its three high schools, were told about the killings Friday morning, then encouraged to talk about it in class or with counselors.
"Some were very quiet, some were reflective, some were more open," said Andrews. "The mood at the schools was very subdued."
"It was just a surprise. It's one of those 'this doesn't happen here' kind of things. It's actually a grim reminder to us all that we're all vulnerable," he said.
But what, if anything, made these four victims particularly vulnerable, leading to their deaths, hasn't been revealed.
Was it a drug deal gone bad? A theft? A fight? Residents want to know, but authorities refuse to speculate.
Casey Cox, the sheriff department's lead investigator, explained that officials want to be careful about what they release, while acknowledging that this case is personal to many: "There's a lot of emotion that goes into this case just simply based on the age of these children."