His first stop is often the library, where he goes to wake up the homeless people camping outside before it opens.
Yet there is a mutual respect to be seen between DeCaprio and the city's homeless. It's a respect he's earned over the last 10 years in his position. In that time, he's watched the homeless population explode from five to more than 300.
He's also seen his department rocked by the beating death of Kelly Thomas, a mentally ill homeless man he knew.
"I had several contacts with Kelly, probably more than 50," said DeCaprio.
One year ago, a security camera caught Thomas' run-in with six Fullerton officers. DeCaprio was not working that night, but he believes his presence could have made a difference.
"The majority of the time I'm successful in gaining voluntary compliance in dealing with them," he said.
Two police officers now await trial for Thomas' death. The controversy also led to the early retirement of the police chief and the recall of three city council members.
DeCaprio now has more help in the form of Cpl. Daniel Solori, who has also been assigned to work with the homeless.
"The police have gotten very sympathetic toward us," said Ken Baen, a homeless man.
All Fullerton police officers have received specialized training in mental illness and homelessness. And two months ago, an Orange County mental health clinician began going on patrol with DeCaprio, bringing services to those in need.
"The fact they've made any change is great for the people," said Ron Thomas, Kelly Thomas' father.
Despite the changes, Ron Thomas is suing Fullerton police and the officers involved in his son's beating, believing his son's death could have been prevented.
"I need change and that's why we're suing," he said.
Fullerton police are not commenting on the pending litigation.
As for DeCaprio, he too would like to see more change, like a year-round homeless shelter in Fullerton. He says the need is hard to ignore, but believes the tragedy has helped bring attention to the problem of homelessness.