Tijuana Mexico

An investigator says federal agents felt trapped when they fired guns at a van packed with suspected illegal immigrants at the nation's busiest border crossing.

San Diego police Lt. Kevin Rooney said Wednesday that the agents were on foot and didn't have an area where they felt they could flee as two vans sped straight at them.

Four people were injured Tuesday after drivers of three vans attempted to storm past inspectors at the San Ysidro port of entry connecting San Diego and Tijuana, Mexico. Two were struck by gunfire, and two others were hurt when one of the vans hit a truck. Rooney says none of the injuries was life-threatening.

Authorities say two drivers were arrested and expected to be charged with smuggling. Another driver fled to Mexico, where he was captured, and will be prosecuted there.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.