DNA lifted from the sheath of a knife found at the crime scene in Gaithersburg, Md., helped lead police to arrest the stepfather of slain 12-year-old Jessica Nguyen.
David Rich Hang, 42, was taken into police custody Monday night.
"This was an absolutely innocent victim ... It just makes no sense why she was killed," Montgomery County Police Chief Thomas Manger said.
DNA was a key piece for investigators, Manger said. A forensic lab matched a DNA swab from Mr. Hang to a sample taken from a knife sheath at the site of the murder. Police believe that knife, which has not been recovered, was used to kill Jessica, who was stabbed more than 40 times.
Chief Manger said a boot print found at the scene matched with Mr. Hang. In addition, police learned that Hang had taken off from work the afternoon of the murder. He is employed as a bus driver for the Montgomery County Ride-On Bus System.
His cell phone puts him in the Gaithersburg area at the time of the homicide. The next day, investigators noticed his hand was extremely swollen.
Hang is currently in the process of divorcing the victim's mother. Police said that he had lived in the house with Nguyen and her mother from 2005 to 2006. Manger said that there were no signs of forced entry at the murder scene, leading police to believe that the perpetrator was someone known to the household.
The chief said in Wednesday's press conference that in addition to Nguyen's mother, Hang had at least one other wife, with whom he was living. Police sources told News4 last night that Hang might have had four or more wives in Montgomery County.
Despite the evidence, neither Chief Manger nor Montgomery County prosecutor John McCarthy was able to identify a motive in the case. Chief Manger seemed to indicate that the girl was an innocent bystander, but said at the time, he could not explain why Hang would kill the girl.
"What troubles me is that you can have someone as cold and heartless as that," Chief Manger said, "who could kill an innocent child that really had nothing to do with whatever issues he had."
It was not a random killing, the prosecution said.
The prosecution alleged that Nguyen's mother had been involved in an "immigration sham-like marriage" with Hang. According to prosecutors, Hang was angry at Nguyen's mother for not living up to the agreement.
"This was an arranged marriage to satisfy immigration consequences," McCarthy said. "I believe he thought he could get out of it at same point in time. He wanted out in order to go on with his life, with his new wife."
Hang was determined to be a flight risk, and was denied bond. The judge said Hang had recently spent time in Nevada, where he used a fake name.
During the bond hearing, Hang said before the court, "I didn't do it."
He faces the charge of first-degree murder.