Officials on Monday deployed side-scan sonar in the search for a 6-year-old boy who was believed to have died along with three male family members after their car plunged into the Chesapeake and Delaware Canal in Middletown, Del., Sunday morning.

Delaware state police said that besides the sonar, the search for the missing boy would involve boats from numerous agencies, as well as Pennsylvania state police cadaver dogs.

All the victims were related, said Delaware State Police Master Cpl. Michael Austin. Police did not release their names at the request of their families.

The victims who died were ages 18, 16, and 12. Relatives identified them to 6ABC, telling the station that the driver, 18-year-old Willis Lindsey; 16-year-old Kyree Lindsey; and the missing boy, Ethan Lindsey, were brothers. The fourth victim, Eric Lindsey, was their cousin.

A 16-year-old girl who has been described as Willis Lindsey’s girlfriend made it to shore after the crash. She told police the 18-year-old saved her and died trying to reach the other three in the Chevrolet HHR station wagon that sank in about 20 feet of water.

Searchers recovered the bodies of the teenagers and the 12-year-old boy on Sunday.

State police are investigating to determine how the car crashed into the canal on its south side, about a mile west of the Route 1 William V. Roth Bridge.

The 35-foot-deep shipping channel connects the Delaware River and Chesapeake Bay.