POLICE yesterday were examining crime-scene evidence for DNA and looking through surveillance videos that may help lead them to the vicious attacker who sexually assaulted, beat and strangled 20-year-old Sabina Rose O'Donnell early Wednesday morning.

Chief Inspector Evelyn Heath of the Forensic Science Bureau said a man's T-shirt and the victim's clothing were found in the grassy lot behind the three-story brick apartment building where O'Donnell lived.

It was in that grassy lot, just north of Girard Avenue, between 4th and Orianna streets in North Philadelphia, where O'Donnell's naked body was found shortly before 10 a.m. Wednesday. Police believe the attack happened between 2:30 and 3:45 a.m.

Heath, standing on North 4th Street yesterday, across from the building where O'Donnell lived with her stepfather, said the crime lab will work this weekend to determine if there is any DNA evidence from the clothing that could lead to O'Donnell's killer. O'Donnell's body will also be swabbed, she said.

This case is "top priority," Heath said, adding she hopes to have some results in a week.

Police Homicide Sgt. Tim Cooney said detectives are looking at city and store surveillance videos from the area. He would not comment on what the videos show.

According to reports, surveillance video shows the victim on a bike, with a person of interest biking in the opposite direction and then stopping to follow O'Donnell, shortly before she was slain.

O'Donnell, who grew up in Philadelphia, was a popular waitress who worked at PYT, a burger joint and bar at the Piazza at Schmidts in Northern Liberties.

"She was my best friend," a woman working at PYT who identified herself as Marie R., 25, said yesterday. "I'm still expecting her to ride over to my neighborhood. We hung out every day."

O'Donnell had been hanging out with friends Tuesday night at El Camino Real, a bar and restaurant on 2nd Street near Germantown Avenue, and later went to a friend's house near Front and Girard. About midnight, she asked to borrow her friend's bike to ride home.

O'Donnell attended the Greenfield School on Chestnut Street near 22nd starting in first grade. She applied and got into the Julia R. Masterman School in fifth grade, assistant principal Mary Ann Tancredi said yesterday.

"It's just heartbreaking," Tancredi said of O'Donnell's death. "She was a beautiful girl, intelligent, with such potential."

O'Donnell left Masterman, on Spring Garden Street, during seventh grade. Tancredi did not know where she went next, but she graduated from Franklin Learning Center on 15th Street in 2007.

"She was a good student," Charles Staniskis, Franklin's principal, said. "She was well-liked by everyone."

Dana Williams, the high school's dance teacher, added: "Sabina was very intelligent. She could have easily gone to college and done very well. She was a dance major here, but she had aspirations of being an actress."

A fundraiser to help O'Donnell's family, being organized by PYT owner Tommy Up, will be held at 10 tonight at Octo Waterfront Grille, on Columbus Boulevard near Race Street ($10 at door).

There is also a $25,000 reward for information leading to the killer's capture and conviction. Tipsters can call 215-546-TIPS.