Police have identified the two suspects as 17-year-old Marvell Hargrove and 20-year-old Quasheam Richburg.
Police say Hargrove and Richburg entered Trax Foods on North Front Street early morning on May 26 with a long rifle in hand.
50-year-old Mustafa Shaker was on duty at the time as the suspects demanded money.
Surveillance video released by police shows Shaker wouldn't open the register.
Police say one of the suspects then shot Shaker in the head.
"The employee puts his hands up, actually backing away, he only says, 'I'm not going to open up the register,' and with that, [the suspect] fires two shots from a sawed off shotgun at a close range," Philadelphia Police Captain James Clark said.
The two then fled the scene.
Mustafa Shaker was the father of two teenagers. His brother told Action News that he moved to Philadelphia from Egypt in 1993.
He began working the overnight shift just a few months ago.
Both Hargrove and Richburg are considered armed and dangerous.
Anyone with information is asked to contact the Philadelphia Police Homicide Unit at 215-686-3334/3335.