Authorities questioned four men Friday for possible involvement in an alleged plot to kill Gov. Jeb Bush and held two others on immigration charges, but by day's end they had all but wrapped up the case after their most promising lead collapsed. The lead: a van investigators thought might contain traces of explosives after bomb-sniffing dogs reacted to it. Late Friday night, residue tests proved negative. Investigators already were skeptical of information provided by a jailhouse informant that four South Florida men with Arab names had plotted to blow up the governor in Tallahassee Friday. Additional information about the inmate ...