A bomb blast near the southern Lebanese city of Sidon has seriously wounded a senior intelligence officer and killed four of his aides and bodyguards.
Col Shehadeh was carried to an ambulance for treatment
Officials said Samir Shehadeh's car was hit by a remote-controlled bomb as he drove past the village of Rmeileh.
Col Shehadeh was an investigator into the killing of former Prime Minister Rafik Hariri in early 2005.
The incident comes amid a fragile truce after 34 days' bitter fighting between Israel and Hezbollah guerrillas.
Both vehicles of Col Shehadeh's two-car convoy were riddled with shrapnel. Police sealed off the area and began collecting evidence.
Government officials said Col Shehadeh was taken to hospital in Sidon and his condition was stable.
Lebanon's acting information minister told Lebanese TV that one of the dead bodyguards had been acting as a decoy for Col Shehadeh in the lead car.
"It is obvious from the decoy operation that saved him that that there were expectations (of an attack)," Ahmed Fatfat told Future TV.
The bombing comes two weeks before the UN chief investigator is to submit a report on his latest findings in the Hariri investigation to the UN.
The Lebanese government is expected in the next few weeks to authorise an international tribunal to bring those responsible to justice.
Col Shehadeh is reported to have been involved in the arrest four pro-Syrian Lebanese generals last August in connection with the investigation.
Earlier UN investigator's reports have also implicated top Syrian officials in the Hariri killing, although Damascus has denied any role in it or the string of bombings targeting anti-Syrian figures which followed the 14 February 2005 assassination.
Mr Hariri's death galvanised Lebanese opposition to Syria, which subsequently bowed to pressure to pull its troops out of Lebanon after nearly 30 years of military presence.