Detectives are investigating whether anybody was to blame for a crash in which a 16-year-old boy died after his mother's car hit a pothole and swerved into a dyke.
Jack Brennan's mother Rachel Edwards, the driver of the car, who was six months pregnant at the time, managed to escape through an open window and swam to the surface.
Mrs Edwards then dived back down to save her two-year-old daughter, Isabella, but was unable to free her son Jack without letting go of the toddler.
The 39-year-old was driving her children through Midville, near Boston, Lincolnshire, last month when the car hit a pothole and veered off the road into the dyke. Two of Jack's friends were also in the car but managed to escape and run for help.
A spokeswoman for Lincolnshire Police said there was a "live inquiry" into the crash. She said: "There is still lots of work to be done to establish what the circumstances were and what happened.
"We will look at the causes to see if anyone was responsible. That's not to say if someone was at fault there would be any further action - that would be up to the Crown Prosecution Service. They need to get to the point where they know what happened on that day and that's an ongoing thing."