According to the police, the incident came to light after a resident of DLF phase one contacted the NGO on March 13 about disappearance of the puppies she used to feed daily.
Amita Singh, the president of NGO -- Walk for Animal Habitat -- said heads of the 12 dogs were smashed with stones and buried in the vacant plots.
"We found bricks from the place and which were probably used to smash their heads," Singh said.
A senior police official said, "An FIR under Prevention of Cruelty to Animals Act and relevant sections of IPC has been registered against unknown persons. Investigation is underway."