A second bomb threat against Stamford schools within one week had parents and students on edge Thursday.

Police say the threat came in at 3 a.m. to the voicemail of the superintendent of schools. They say schools were not closed because the threat was not considered credible. Schools were put on alert, and after-school activities were canceled as a precaution.

Stamford Police Chief Brent Larabee says police know who the caller is. He says police do not believe he is capable of doing harm, but they are building their case against the individual.

The bomb squad detonated a mysterious object on Westover Elementary School?s athletic field after someone reported seeing it placed there. The object was deemed not to be explosive. Police reaction was an effort to remain diligent in light of the larger threat.