PHILADELPHIA—Police in Philadelphia are investigating three shooting deaths in different parts of the city in less than 12 hours.

Officers were called to the Kingsessing neighborhood in southwest Philadelphia early Tuesday on a report of an illegally parked vehicle—and they found a man in his 20s shot to death inside.

About two hours later, officers were called to northeast Philadelphia, where a man had been shot while walking in the Kensington neighborhood. He was later pronounced dead at Temple University hospital.

On Monday evening, police said a masked gunman followed a 21-year-old man into a north Philadelphia grocery store and shot him to death execution-style.

In all three cases, officers said they hoped surveillance video from cameras in the area would lead them to a suspect.