Sabina Rose O'Donnell had just four blocks to go. When she left a friend's apartment at Front Street and Girard Avenue shortly after midnight, she was a five-minute bike ride from home.

The popular 21-year-old waitress never made it inside.

Her nude body was found Wednesday morning in a lot behind the apartment she shared with her stepfather in the 1200 block of Fourth Street, on the northern edge of Northern Liberties.

O'Donnell suffered blunt-force trauma to her face and body and was apparently strangled, Capt. James Clark of the Homicide Unit said. One law enforcement source said a piece of her clothing had been found wrapped around her neck.

There were no indications that O'Donnell knew her killer, Clark said, and police had no leads Wednesday night. Investigators hoped to look at surveillance footage from the area and were talking to neighbors who may have heard something.

"This was savage and brutal," Clark said of the killing. "This person is someone we need to find as soon as possible."

Police believe the killer approached O'Donnell in front of her house, then dragged her to a lot on Orianna Street, about a half-block off Girard.

Clark would not comment on whether O'Donnell had been sexually assaulted, pending the medical examiner's report, but law enforcement sources said there were signs she had been raped.

At a vigil Wednesday night at Fourth and Girard, several dozen of O'Donnell's friends gathered to share memories. They said she had taken lots of pictures and loved going clubbing and out to dinner.

They cheered for her, saying, "To Sabina!" "We love you, girl!"

One friend spoke about having dinner with O'Donnell Tuesday night, a meal that included O'Donnell's favorite bottle of wine.

"She said, 'We don't deserve this life,' " the friend said. "I'd like to think she really enjoyed that last bottle."

O'Donnell's friends urged each other not to go home alone, and to watch each other go in their houses.

O'Donnell frequented the Northern Liberties neighborhood that has in recent years become one of the city's hottest areas for young hipsters, artists, and professionals to live, shop, and bar hop.

O'Donnell worked at PYT, a lounge and burger joint in the Piazza at Schmidts, which was closed Wednesday in her memory.

Owner Tommy Updegrove posted on Twitter, "PYT is closed tonight for a death in our family. We love you guys."

Debbie Renta, who lives with her family across the street from where O'Donnell lived, said the killing made her more concerned for her 20-year-old daughter.

"She comes home alone. Sometimes I do, too," Renta said. "Who could have done this to that girl? I hope they catch him."

O'Donnell spent Tuesday night out with friends in Northern Liberties, going first to El Camino Real restaurant around 7:30 and then next door to Bar Ferdinand.

Around 10 p.m. she and a female friend went to the friend's apartment to watch movies and hang out, Clark said. Around midnight, O'Donnell asked to borrow her friend's bicycle and pedaled home.

A neighbor walking a dog found O'Donnell's body shortly before 10 a.m. She had been robbed, police said, and the contents of her purse were strewed around the lot.

O'Donnell's purse was missing, but it had been found shortly before 7 a.m. Wednesday near Fourth and Girard by a woman on her way to a bus stop.

The purse was on the curb near the intersection, and the woman, who asked not to be named, picked it up and looked for identification. Inside she saw pictures, change, pay stubs, and a wallet, which was open and empty.

The woman took the bag to a mailing store and sent it to the address she found on the pay stubs.

"I packaged it up, put it in a bag with a note saying I'd found it, and that I hoped everything was OK," she said. "Now I feel stupid that I said that."

Moments after sending the purse, the woman learned of O'Donnell's death from a friend and recognized the name. She then returned to the mailing store, retrieved the purse, and called police.

Last June, Rian Thal, 34, and Timothy Gilmore, 40, were shot and killed outside Thal's apartment at the Piazza at Schmidts. Police have said they were involved in drug dealing.

Anyone with information in O'Donnell's killing is asked to call the Homicide Unit at 215-686-3334.