The fact that they were found in a building under construction means nothing, unless you believe that builders in Lebanon work 24/7. It may come as a shock to you but the Israelis have a habit of dressing as Arabs in order to carry out their little "exploits". You do recall the "Arabs" who carried out the bombing of the King David Hotel? What would be interesting to know would be how long were the timers set for, if more than about ten mins then it would be proof that the Israelis set them.
17-year-old Palestinian killed by IDF on Friday laid to rest near Ramallah (Haaretz)
from the article: Lebanon army dismantles 4 rockets aimed at Israel