Police on Thursday released surveillance footage that shows the final minutes before 20-year-old Sabina Rose O'Donnell was killed last week, and the man who appeared to follow her before she died.

The footage, captured by several security cameras around Northern Liberties and Fishtown, depict a young man biking around the neighborhood for almost an hour. At one point, O'Donnell can be seen biking past him, pedaling in the opposite direction down 4th Street near Girard Avenue, and the man turns his bike around to follow her. That footage was recorded shortly before 3 a.m. June 2, the time when police believe O'Donnell was killed.

Police asked for the public's help in identifying the man, who they described as a "person of interest." In addition to the camera at 4th and Girard, he was filmed by cameras at Front Street and Girard and 5th and Girard. Police believe he may have been trawling for a potential victim, said Philadelphia Capt. James Clark.

"Hopefully somebody saw him out there," said Clark, who said police believe O'Donnell's killer lives in her neighborhood.

O'Donnell was strangled in a lot behind her apartment building, near 4th and Girard. Police believe a stranger saw her biking home, snatched her off the bike and dragged her to the lot. She was beaten and sexually assaulted.

A $25,000 reward has been established for information leading to the arrest and conviction of O'Donnell's killer. Call police at 215-686-3334 or 215-546-8477 (TIPS) to make an anonymous report.

Contact staff writer Allison Steele at 215-854-2641 or asteele@phillynews.com