Investigators searched the rubble of a car-bombed building in Beirut for clues to an attack yesterday that boosted fears of renewed bloodshed in Lebanon and complicated already troubled negotiations between rival political groups over the formation of a new government. The explosion wounded nine people and devastated an eight-story apartment building in the largely Christian New Jdeideh neighborhood shortly after midnight, sending panicked residents in their pajamas into the street. It blew off the fronts of some structures, left a seven-foot-deep crater, damaged parked cars and shops and shattered windows for several blocks. The motive behind the attack wasn't immediately clear. In response, the army announced stricter measures against any security violators. "The army will not allow that freedom of expression be abused in order to harm security and stability," a military statement said. The bomb came amid the withdrawal of Syrian troops to eastern Lebanon and Syria after a 29-year presence in this former civil war-ravaged country.