LAMONT WALLACE was ambushed outside a corner store after buying cigarettes. Armed muggers jumped Jonathan Bell and Rolando Lugo-Almonte. And Christopher Foster was dragged into a car at gunpoint in Roxborough and dumped dead in Germantown.

These cases represent just a fraction of the more than 90 homicides in 2011 that remain unsolved. City police are seeking the public's help to crack them:

* Christopher Foster, 18, was a Roxborough High School senior who went with a friend to grab a sandwich on Jan. 19. On the way, two black men pulled up in a green Cadillac, waved a shotgun and forced Foster inside. A short time later, police found Foster's body with a single gunshot to his torso - and facial injuries suggesting he'd been beaten - on Woodlawn Street near Morris.

* Lamont Wallace, 21, worked at the stadiums and hopped a subway home after a game on March 30. Just before 1 a.m., he stopped in a convenience store on Marvine Street near Parrish in North Philly for cigarettes. Chatting on the phone with his cousin as he left the store, he said: "I think I'm going to have a problem. . . . Here we go." The cousin told police he heard a struggle, Wallace pleading for his life, then gunshots.

* Porfirio and Juana Nunez and Lina Sanchez. Porfirio Nunez was about to close his corner store, Lorena's Grocery, at 50th and Parrish streets in West Philly, on Sept. 6 when two men burst in and repeatedly shot him, his wife, Juana, and her sister, Lina, during a robbery. This case carries a $25,000 reward for tips leading to the capture and conviction of the killers.

* Rolando Lugo-Almonte, 23, had locked up his LaMecca Food Mart, at 15th and Wharton streets in South Philly, at 8:30 p.m. Nov. 23 when two men in hoodies announced a robbery. The robbers shot Lugo-Almonte repeatedly in the chest and stomach and fled on foot. Lugo-Almonte died 90 minutes later at the Hospital of the University of Pennsylvania.

Anyone with information on any of these cases is urged to call the department's tip line at 215-686.8477.