A retired police officer will face gross misconduct proceedings over his handling of a fatal crash investigation.
Jacob Crawshaw, 19, of St Neots, Cambridgeshire, died when the work van he was a passenger in crashed on the A14 in Northamptonshire in October 2021.
During the case, the driver was drug tested too late to establish whether he was under the influence at the time of the incident.
The Independent Office for Police Conduct (IOPC) found there was "a case to answer for gross misconduct", and papers were served to former Det Con Ady Tredwell.
His representative and Northamptonshire Police said they could not fully comment, citing an ongoing investigation arising from the IOPC's review.
The van driver, Christopher Hicks from St Neots in Cambridgeshire, was convicted of causing death by careless driving, but a drug test, which was positive, was only carried out the day after the crash.
Jacob had sent a text to a friend minutes before the collision, which stated: "My driver is stoned. Lovely".
The IOPC review came about at the request of the Crawshaw family.
The watchdog's report, seen by the BBC, also detailed failures in the way the force investigated itself following a previous complaint from Jacob's parents, Tracey and James.
According to the IOPC, Northamptonshire Police had initially decided Det Con Tredwell had a case to answer for gross misconduct, but decided not to pursue it as he had been medically retired.
However, the watchdog concluded that proceedings could still be brought.
The IOPC also directed the force to investigate the actions of his superiors, which it said had not been examined adequately.
Had they provided better oversight, "issues might have been identified earlier, potentially preventing some of the subsequent mistakes in the collision investigation".
It was also understood that discussions were underway into a potential review by His Majesty's Inspectorate of Constabulary and Fire & Rescue Services (HMICFRS).
This would look at Northamptonshire Police's road traffic investigation processes, and whether it had learned lessons from the Crawshaw case and the death of 19-year-old Harry Dunn in 2019.
Mr Dunn's motorcycle collided with a car being driven the wrong way by an American diplomat outside RAF Croughton on the B4031.
Anne Sacoolas was not drug tested and was allowed to leave the scene before flying back to the US under diplomatic immunity.
She eventually pleaded guilty at the Old Bailey, via videolink, to causing his death by careless driving.
Reacting to the outcome of the IOPC review, Jacob's mother said: "We are living every parent's worst nightmare".
Mrs Crawshaw added: "We now know that he, and we as a family, were badly let down by Northamptonshire Police. We feel totally vindicated by the IOPC report."
"Jacob deserves justice, and we expect accountability".
Radd Seiger, an adviser to the family, praised their "tenacity".
"It is shocking to see the failings in Jacob's case and how poorly the case was investigated, leading to a serious miscarriage of justice," he said.
Mr Seiger continued: "When Jacob's family complained, the failures were minimised and swept under the carpet".
Former Det Con Tredwell was served the notice via the Northamptonshire Police Federation.
Chair Sam Dobbs said: "This is a very sad case which has to be investigated within all the requirements. The former police officer and the Police Federation clearly can't, and shouldn't, make any public comment whilst there is a live investigation".
A Northamptonshire Police spokesman said: "We acknowledge the findings of the IOPC in relation to this matter and continue to engage with the family of Jacob Crawshaw.
"As this remains a live investigation, we are unable to comment further at this time."