They found Robert Bischoff by sharing his photo with a Sinclair gas station clerk who often sold him cigarettes.

They met Alexander Jacob after sending his mom a letter, even though he almost didn’t respond because he figured it was “trash mail.”

The two men and more than 250 more people — all homeless and high-frequency users of jail, detox and emergency departments at taxpayer expense — have been tracked down by Colorado Coalition for the Homeless and Mental Health Center of Denver outreach workers and given apartments through Denver’s social-impact bond program. About two years into the five-year program, researchers have noted a dramatic drop in jail days.

It’s part of the “housing first” model, meaning the first step is providing housing in the hopes that substance-abuse and mental-health treatment will follow.

Among those selected through a Washington, D.C.-based research institute that analyzed jail and hospital data, 60 now live at the Mental Health Center of Denver’s Sanderson Apartments, where natural light floods the hallways and outdoor gardens offer quiet space. Nearly all have substance abuse and mental health struggles. About 10 residents have drug addictions deemed “problematic” by housing and residential services director JoAnn Toney, but that’s expected with residents beginning “their recovery process with the housing piece,” she said.

“You take them just the way you found them,” she said. Only those who are registered sex offenders or have been busted for cooking meth are prohibited from living at Sanderson, which opened as one of the nation’s first “trauma-informed” structures last August. Almost half the residents have started working, at least part time, Toney said.

The apartment staff’s first goal is to gain the residents’ trust, then offer services, which typically happen at one of the Mental Health Center’s clinics. Substance abuse or mental health counseling take place away from the apartment to keep residents’ sense of home separate from treatment that could trigger painful emotions.

“When they’re here, it’s peace,” said program manager Takisha Keesee.

Many residents have not been diagnosed with a mental health issue, but “people who have lived on the streets for as long as they have, their survival instincts are heightened,” Keesee said.

To create the list of people eligible for the program, the Denver Police Department selected those with eight or more arrests in a three-year period, including three arrests in which the person was marked as “transient” because they either gave no address or used a shelter address. People awaiting sentencing for unresolved felonies were screened out.

Among the first 100 chosen, 84 were men, and the average number of arrests was 16 per person from 2013-2015. Because there wasn’t enough housing for all of them, the project’s research partner — Urban Institute — chose people randomly through a lottery.

To find them, outreach workers from the homeless coalition and the mental health center used “global information system” mapping, drawing data and photos from police contacts, electronic health records and client information from the “homeless management” IT system for housing.

The maps revealed the most likely places, down to the street corner, where outreach workers would find who they were looking for, and they set off distributing photos. Typically, these were shelters, abandoned lots and convenience stores. Outreach workers also visited the jail weekly to connect with people on the list who were recently arrested.

When Bischoff walked into the Sinclair station, the friendly clerk told him, “I got your picture!” and dialed the phone number on the business card the outreach workers had left with her. The case mangers arrived soon after and picked up Bischoff.

The connection came after two failed attempts. Bischoff first heard of the housing opportunity when an outreach worker visited him in jail several weeks earlier. Another time, his dad in Boston received a call from the program and told Bischoff. He ignored both.

“I thought there must be a catch,” he said. “I didn’t pay it any heed.”

Last week, Bischoff, 36, was boiling spaghetti in his tidy studio at Sanderson Apartments, a copy of Bill O’Reilly’s “Killing Jesus” turned upside down on the kitchen counter to hold his place. Bischoff’s father mails him five or six books each week, and Bischoff, who completed a year and a half at Northeastern University, polishes off nearly one per day. The bookshelves are full, with Mark Twain, John Irving, Ronald Reagan and Gov. John Hickenlooper. He keeps a Junior League cookbook above the stove, where he is often cooking eggs or pasta for others in the apartment building.

Bischoff, who has social anxiety and bipolar disorders, had been sleeping in the Crossroads Center, a shelter run by the Salvation Army, and working as a maintenance man at a McDonald’s south of downtown. He had been homeless off and on for six years, following a split with his wife that led him to abusing painkillers and heroin.

“I couldn’t get my own two feet under me,” Bischoff said. Now, he’s off drugs and hoping to finish his college education, he said. “It’s a blessing. It’s one of the best things that could ever happen to me.”

Another Sanderson Apartment resident, Jacob, learned of the housing opportunity through his mother, who for years had lived in fear because of his heroin addiction. She called Jacob, 25, to give him the news. “I thought it was trash mail,” he said.

But he called the number anyway. Three weeks later, in September, Jacob was among the first to move into Sanderson Apartments. By then — after years addicted to heroin, “signing” for money at Colorado Boulevard and Interstate 25, and sleeping under a highway underpass — Jacob had started methadone treatment.

Before the methadone, he had gotten clean for weeks or even months at a time after landing in jail or locking himself in his mom’s basement. But he would always return to heroin. Jacob said he finally decided to try methadone after he “got thrown in jail for the millionth time” and was tired of “scaring the (expletive) out of” his mother.

Each day, Jacob makes a three-hour round-trip journey by bus from his apartment to his methadone clinic for his daily dose of the medicine that curbs cravings. He’s looking for a job at a restaurant, which has proved harder than he imagined, even though he knew his resume was spotty, with stints at a KFC and towing company.

“I thought I could dress up, do my hair, take the earrings out and I pretty much assumed I could get a job as a food runner. That’s not the case. They can tell there is something off about me,” he said, after a string of interviews with no offers.

“If I don’t have a job, I can’t feel good about myself,” he said. “I want to feel like a respectable member of the community, instead of just taking and taking.”

Jacob, a conversationalist with side-swept, black hair who often chats with apartment staff, has earned special permission for his girlfriend to stay overnight. He expected the apartment building would look like a “beat-up, bed bug-infested joint” and was blown away by Sanderson. “There is so much glass. They put priority into natural light,” he said. “And the lobby, it’s like some type of Four Seasons.”

After the first full year of the program, the data is promising. A final report, though, isn’t expected for a couple more years.

The city paid $188,000 in October, the first payment to philanthropic foundations and a national bank that fronted about $8.6 million in funding for the five-year program. Under the unique funding model, the program fills in the gaps for costs not covered by federal housing vouchers, Medicaid government insurance and other resources. The investors’ return will depend on how well the program keeps participants out of jail, the emergency room, detox and other services.

In the first year, 64 of 100 people had not returned to jail. Among the 36 who did, most went to jail two times or less, and some because of warrants they had when they were selected for housing. After one year, 89 out of 100 people remained in housing.

The average length of time between finding a person and signing them up for the housing program was three days, though 83 out of 100 signed up on the day they were found.

The project busts the perception that people who have been homeless for years are resistant to services, “that they are not going to engage,” said Tyler Jaeckel, who coordinated the program’s development in the city’s finance department. “The dynamics are completely different when you offer someone actually housing,” he said.

“It’s been a pretty amazing feat.”