NORFOLK, Va. (WVEC) -- The Navy is turning up the heat, trying to find whoever's responsible for calling in a series of bomb threats earlier in the week.

On Friday, NCIS upped its reward to $2,500.

On Wednesday morning, Naval Station Norfolk received a bomb threat on the phone. Then later that same day, JEB Little Creek-Fort Story received five additional bomb threats.

And Thursday, someone wrote a threat on a wall inside a bathroom at Norfolk Naval Shipyard.

The Navy did not find any devices.