Man, woman both fatally shot in head in Philadelphia, double homicide investigation underway

A double homicide investigation is underway after two people were found lying together on a road in Philadelphia, both fatally shot in the head, authorities said.

It appears both victims were shot "execution-style" near the historic Mount Pleasant Mansion in the Fairmount Park neighborhood, Philadelphia police chief inspector Scott Small said, according to Philadelphia ABC station WPVI.

Krystina Chambers, 38, and Thurston Cooper, 49, were both pronounced dead at the scene at 11:12 p.m. Thursday, Philadelphia police said.

Both were shot in the head, and the woman appeared to be "shot in the head and chest, and the spent shell casings -- the three of them -- are all just a few feet away," Small said, according to WPVI. "So we know at least three shots were fired from a semi-automatic handgun or handguns."

No motive is known and no arrests have been made, police said.

A $40,000 reward has been offered. Police ask anyone with information to call the Homicide Unit at 215-686-3334.

ABC News' Ben Stein contributed to this report.