Under the law, Minehart had to begin the trial Thursday and hear from at least one witness to "lock in" Crespo's decision so he cannot later decide he wants a jury trial.
Defense attorney Michael F. Giampietro said Crespo "insists he is innocent" and chose a nonjury trial only to escape the threat of a death sentence if a jury found him guilty of first-degree murder. Only a jury has the legal authority to sentence a person to death.
"Our intention is to vigorously defend him against these allegations," Giampietro said.
Maldonado's rape and murder was one of the coldest of Philadelphia's cold cases until last April, when authorities announced Crespo's arrest.
Crespo, 47, was serving time in a Florida prison for sexually assaulting a 12-year-old when his DNA matched that found Oct. 2, 1996, on Maldonado's body.
Philadelphia homicide detectives had asked the FBI to check DNA from semen recovered from the victim against samples in the FBI's Combined DNA Index System (CODIS).
Crespo's DNA, added to CODIS in the Florida case, matched to a statistical probability of one in 38 trillion Hispanic males, prosecutors said.
At Crespo's preliminary hearing last June, Vega introduced a statement Crespo allegedly gave a homicide detective in a May 30, 2012, prison interview in Hardee County, Fla.
According to the statement, Crespo accosted Maldonado at Front and Norris Streets as she walked to school Sept. 30, 1996.
Crespo said he had argued with his wife and spent the night drinking, and was looking for a prostitute; he claimed Maldonado offered to have sex with him for $20.
Crespo said they had sex for about 45 minutes in an abandoned house in the 1700 block of North Hope Street. At one point, Crespo allegedly told detectives, the girl asked him to choke her during sex. When she fell unconscious, Crespo's statement continues, he left her there, but he insisted he did not know she was dead.
Maldonado's autopsy showed she died of strangulation, but also was struck in the face, dragged around the floor, and hit at least twice in the head with a blunt object, possibly a hammer, that cracked her skull.