NETANYA, Israel - Israeli authorities launched a full-scale investigation into Thursday night's deadly gas explosion that killed four and injured dozens more.

Three of the building's tenants were still unaccounted for Friday morning.

The blast destroyed most of a four-story apartment building, which housed businesses on the ground floor, in the coastal city's downtown area. The massive explosion also demolished a restaurant and synagogue.

Police arrested a "metal thief" and gas technician in connection with the blast. Both men will appear in district court Friday for an arraignment hearing on possible charges of negligent homicide.

The first suspect, Rami Gueta, was spotted in the vicinity of the explosion with several iron pipes in his possession police suspect may have come from the building.

The second man, gas technician Yisrael Daniel, was dispatched to the building reportedly to repair the damage caused by Gueta.

Home Front Command and rescue workers continued searching through the rubble Friday to make sure no survivors were trapped in the ruins.

Investigators ruled out a terror attack, but have yet to determine whether foul play, negligence or both were responsible for the deady incident.