POLICE Crime Scene Unit investigators returned yesterday to the gritty North Philly gully where a human jawbone was found last week - and this time, they discovered a possible grave.

A law-enforcement source told the Daily News that a piece of slate covered a hole that dropped about 2 feet below ground, and looked to be long and wide enough to fit a human body.

The possible grave was empty. The source said the slate was camouflaged by some of the weeds and trees that wrap around the plot of land, situated behind a ballfield at 4th and Westmoreland streets, that cops have been canvassing for several weeks as part of an ever-growing investigation into disgraced ex-homicide detective Ronald Dove.

The jawbone was found Friday at the site, which investigators believe might have served as a burial ground for Reynaldo Torres, who's been missing since last year. The possible grave was found about 5 feet from where the jawbone was spotted, the source said.

Investigators came across dog and cat bones yesterday, but no other human remains.

Dove, 41, was booted from the force by Police Commissioner Charles Ramsey on Nov. 8 for failing to cooperate with detectives who were probing his involvement in three murder cases:

*  The Sept. 8 stabbing death of Cesar Vera, the ex-boyfriend of Erica Sanchez, Dove's longtime lover. Sanchez, 33, was jailed last month on murder charges.

* The July 1, 2010, fatal shooting of Leslie Delzingaro at an Olney bar that was owned by Sanchez's father. Dove was assigned to the case - which has never been solved - and Delzingaro's family has since filed a complaint with Internal Affairs raising questions about a conflict of interest.

*  The May 2012 slaying of Melanie Colon. She was last seen with Torres, who has since vanished. Based on information on Dove's iPad, investigators are exploring the possibility that Torres was killed, too, and possibly buried - and covered in cement - in the area where the possible grave was found yesterday.