After repeatedly denying knowing Vanessa Pham, Julio Blanco Garcia admitted being her killer in a few dramatic moments as two Fairfax County police detectives questioned him in a cramped interview room.

The detectives told Blanco Garcia that they had overwhelming evidence against him, but they also pleaded with him to provide Pham’s mother with answers to the mystery of why her daughter was stabbed to death. “The bottom line is the gig is up,” one said.

Blanco Garcia, 27, of Falls Church, sobbed in the videotaped interrogation, which was played for a jury on the third day of his murder trial in Fairfax County, and the story of the 19-year-old college freshman’s slaying on June 27, 2010, spilled out. He said he approached Pham at the Fairfax Plaza Shopping Center in Falls Church after he had smoked too much PCP. He was in distress and had his 1-year-old daughter with him, he told the detectives.

“I’m not a bad guy,” Blanco Garcia said on the video, recorded after his arrest. “I was just so high that time. . . . I asked for a ride to the hospital and I grabbed a knife. . . . I’m so sorry I didn’t mean to. . . . God is not going to forgive what I did.”

Blanco Garcia explained that he was hallucinating. He said that Pham had taken a wrong turn on the way to the hospital and that he thought he and his daughter were in danger. He said he also feared that she might call police, so he grabbed a large butcher knife from his backpack and stabbed her.

“She was crying,” Blanco Garcia said on the video. “She didn’t say anything.”

At that point in the recording, Blanco Garcia cried uncontrollably, and his head fell into his hands. In the courtroom, Blanco Garcia turned away from a screen as the video played. He barely moved.

After the stabbing, Blanco Garcia told detectives in the interrogation, he tried to drive Pham’s car but ran it off the road near Arlington Boulevard, a short distance from where Pham had picked him up that Sunday afternoon. Blanco Garcia said he then grabbed his daughter and scrambled out of the car’s sunroof and caught a bus home. He said he washed the blood from his hands with a baby wipe.

Pham’s car was spotted shortly after the killing by a passing motorist, touching off a 21 / 2-year search for her killer. Blanco Garcia was not a suspect in the case until after he was arrested for shoplifting in 2012 and his fingerprints were taken. His prints matched those found on the knife used to kill Pham.

Blanco Garcia said on the video that he always suspected he would be caught. The killing weighed heavily on him, he said, and he turned to heroin to numb himself.

Prosecutors have asked the jury to find Blanco Garcia guilty of first-degree murder. Blanco Garcia’s attorneys have not contested that their client killed Pham but said it was the result of a “perfect storm of tragedy,” not premeditation.

A forensic expert also testified Wednesday that DNA found on the knife used to kill Pham probably came from Blanco Garcia. In separate testimony, a Fairfax County police detective said a search of Blanco Garcia’s computer showed that it was used to track the investigation into Pham’s killing via news Web sites — including The Washington Post — and social media. There were also Web searches for PCP, heroin, weed and drug addiction.

Timeline: The slaying of Vanessa Pham

Toward the end of his interrogation, Blanco Garcia said he would trade his life for Pham’s, if he could. He apologized again for killing Pham.

“Many times I thought about telling police, but I didn’t want to leave my family,” Blanco Garcia told the detectives. “I asked her to take me to hospital. She took me. She had a good heart. That’s why I feel so bad.”

The Washington Post will provide coverage throughout the trial. Follow reporter Justin Jouvenal, @jjouvenal, on Twitter for live updates.