sentences:  The rebels headed toward Chechnya in a column of eleven buses and two trucks, but were stopped short of the border between the two republics when a Russian attack helicopter opened fire on the convoy's lead vehicle which was a Dagestani police car escorting the column.According to some reports the border bridge was blown up as well, but journalists later reported it intact.The Chechens captured 37 Novosibirsk OMON special-police officers, who surrendered at a border checkpoint.