NEW CASTLE COUNTY, Del. (CBS) — Authorities in Delaware are resuming their search for a 6-year-old boy missing after an SUV plunges into a canal, killing three of his family members. Police say the SUV, driven by 18-year-old Willis Lindsey, plunged into the Chesapeake and Delaware Canal in New Castle County on Sunday morning.

Willis’ girlfriend, his younger brothers, ages 16 and 6, and a 12-year-old cousin were in the vehicle at the time. Authorities recovered three bodies on Sunday but could not find Lindsey’s 6-year-old brother.

The missing 6-year-old boy is presumed to have drowned.

(Credit: CBS3)

During a press conference Monday morning, Delaware State Police said they will continue looking for that little boy’s body until they find him.

“The search and recovery mission is still in progress,” Delaware State Police Master Corporal Michael Austin said.

Delaware State Police said they are using sonar technology to locate the 6-year-old’s body. They also urged the public to not be in their way.

“As of right now, we respectively and graciously decline their offers but we appreciate their efforts, we appreciate their thoughts. Right now, the best thing and the most efficient thing is to let the professionals do their job and to keep as much distractions and traffic out of the area as possible,” Austin said.

The sole survivor of the crash, the 16-year-old girl, told police Willis helped her to shore. Lindsey then went back underwater to rescue his two brothers, as well as their 12-year-old cousin. But Lindsey never resurfaced.

Investigators are still working on figuring out what caused the 18-year-old driver to lose control. Family members say they were never supposed to be on the gravel road. They say the boys probably got lost and tried turning around before the deadly accident.

A GoFundMe page has been set up to help the family.

CBS3’s Matt Petrillo contributed to this report.