He could become the Willie Horton of the immigration crisis.

Milton Mateo Garcia, 28, was caught one year ago entering the U.S. illegally across the Mexican border and was deported back to his native Honduras.

But Mr. Garcia soon re-entered the U.S. illegally — federal authorities either don’t know how, or they won’t say. He settled with relatives in Philadelphia, where Mayor Michael Nutter had signed an executive order in April declaring it a “sanctuary city” for illegal immigrants.

Since then, it’s the city’s official policy to defy federal authorities seeking to deport illegal immigrants unless the person sought by the U.S. Immigration and Customs Enforcement agency has been convicted of a violent felony. More than 100 communities nationwide have enacted similar policies, with the tacit blessing of the Obama administration.

Living and working in sanctuary, Mr. Garcia last month, according to police, approached a 26-year-old Philadelphia doctor who was walking to her home in the city’s fashionable Rittenhouse Square neighborhood after a night out with friends. He is accused of forcing the woman into her apartment and raping her repeatedly.

Police said Mr. Garcia then stole the victim’s cellphone and rode away on his bicycle. In perhaps not the smartest of moves, Mr. Garcia kept the victim’s smartphone in his possession. Police said they found him, in part, by calling the phone and locating its signal.

With Mr. Garcia now in prison facing trial on rape, kidnapping and robbery charges, ICE has lodged a detainer against him, requesting that local police notify federal immigration authorities before he would be released. But Philadelphia police won’t honor that request unless Mr. Garcia is convicted of a violent felony and a judicial warrant is issued.