The FIRST thing you or a mechanic needs to check it what the puncture/hole looks like and its location. Without that information you get a lot of guessing about the cause and cure. From the above it looks like he did that and it should not be hard to figure out the problem from there, but the exact nature of the puncture is important.

The most common are:
1. Hole/pinhole or short slash next to tread area - road hazard
2. "Snakebite," two short parallel punctures - Rim cut from pothole or other obstruction, more common with underinflated and low profile/width tires.
3. Hole or curved cut next to rim - spoke or rim hole (on double walled rims) puncture.
4. Small bubble with curved puncture next to rim and near valve stem - underinflation, tube migrates until it stretches and fatiques on one side of valve. Other side of valve will typically have a crinkled section of tube.
5. Valve cut - underinflation, valve gets so crooked that rim hole cuts it.
6. Very long split in tube or star shaped hole - Blowout, tire not seated, tube under bead, overinflation or large hole allowed tube to escape.

p.s. If you use the rim nut on a presta valve make sure you keep the tires inflated. Otherwise the tube (esp on the rear) can migrate and because the valve is held in place it will stress the tube and cause #4. NOT likely the op's problem, as it happened even without the tire mounted or ridden.