Police couldn't immediately say how the teen managed his escape, reported about 1:40 p.m., from the state-licensed Provo Canyon School, which is a secure, locked facility.
Once out, the teen allegedly broke into the home of Provo resident Andrew Alger.
Alger returned about 4:30 p.m. to find his iPad out of its case and charging from the printer. As he tried to figure out what was going on, he heard his bedroom door open and saw the teen, who he described as 6-feet-2-inches and African-American, standing "in the entryway to the bedroom, wearing my clothes."
Alger froze. The teen spoke first.
"He said, 'Sir, I'm really sorry that I'm in your house,' " Alger said Monday. The boy appeared to have been there a while, judging by an empty Capri Sun drink container and the bedroom in disarray.
Confronted with the apologetic intruder, Alger ordered the teen to empty his pockets of Alger's cash and spare car keys. The teen claimed to have been kicked out of his aunt's house. Alger told him to leave Alger's shoes but allowed him to keep the clothes.
"He was kind of sad, kind of moping a little bit. He walked down the driveway and sat and kind of thought about what he was going to do next, I imagine," he said. Alger then called the police.
The runaway didn't seem like a hardened criminal, Alger said.
"I hope that he would have gone back and turned himself in. Now he's facing what he is. He's a younger kid. I feel bad and I feel sick for the family" of the crash victims, he said.
When he left Alger's house, the teen headed east to an underground apartment complex parking garage, where he found a black Mercedes SUV with the keys inside, Post said.
The boy drove back to the school in the stolen car. Provo Canyon staff called police again about 8 p.m., when they saw him in the parking lot. Officers spotted the car near 1800 N. Freedom Blvd. and tried to pull it over, but the teen drove away, turning southbound on University Avenue.
He was initially going the speed limit, but accelerated near Bulldog Boulevard and started weaving in and out of traffic. Following department policy to avoid high-speed chases unless the driver is suspected of an aggravated or forcible offense, officers turned off their overhead lights and stopped following him about 15 blocks from where the chase began.
The boy continued to speed on University Avenue until he hit the SUV, which was stopped at a red light at 1860 South, about 20 blocks away from where police ended the chase.
Uninjured, the teen bailed out after the crash and ran, but a Provo police sergeant who was on his way to work and saw the accident from Interstate 15 chased the teen and caught him.
He was arrested and booked into Slate Canyon Detention Center on suspicion of burglary, vehicle theft and manslaughter. The teen who is from out-of-state has a prior criminal record, but details and his name weren't released due to his age, Post said.
The Provo Canyon School in a statement said they were "deeply saddened by this tragedy and our heartfelt condolences go out to the family of those involved."
School officials said they take the safety and wellbeing of their patients very seriously and have been cooperating with authorities and the ongoing investigation.
They said they couldn't discuss the teen's situation because of privacy laws. They did not address how the teen escaped or how quickly school employees reported the teen's disappearance.
Post said officers have responded to the school on reports of runaways before, but "nothing of this magnitude."
Elizabeth Sollis, spokeswoman for the Utah Department of Human Services, which contracts with the school, said the state plans to review the incident to ensure that the school followed policy.
Reporter Janelle Stecklein contributed to this report.
What is Provo Canyon School?
Utah Department of Children and Family Services contracts with Provo Canyon School, a residential treatment center for troubled teens that can house up to 130 male clients. The school also contracts with California and Washington D.C., in addition to accepting private clients, including those funded by school districts and Medicaid.
Source: Elizabeth Sollis, spokeswoman for the Utah Department of Human Services