The body of the 18-year-old was discovered when police were called to the city’s Galliagh area after a car crashed and caught fire on Saturday, June 1, 2019.
It later emerged that the teenager had not been seriously injured by the crash and was still alive when the red Mazda 6 saloon car caught fire.
The PSNI senior investigating officer Michael Winters has issued a fresh appeal for information in advance of a BBC radio documentary about the case.
Detective Inspector Winters said police were keen to hear from anyone who could help with what he described as “very much a live investigation”.
It is believed at least two other men were involved in the incident but fled the scene.
“The body of 18-year-old Caoimhin Cassidy was found inside a Mazda 6 which had crashed on the Fairview Road during the early hours of Saturday, June 1, 2019.
“Initially it was believed that the car had caught fire as a result of the collision.
“However, the results from the post mortem examination subsequently told us that Caoimhin was not seriously injured as a result of a crash and was most likely still alive when the blaze started.
“We believe that Caoimhin was not travelling alone in the vehicle,” DI Winters said.
The PSNI officer asked anyone with information about Mr Cassidy’s movements or those of the car to get in touch. The vehicle was stolen earlier on the night of Friday May 31 from a house at Oakfield Crescent.
Mr Cassidy’s death is to feature in “Assume Nothing: The Boy in the Burning Car” radio documentary.In episode one, journalist, Una Kelly investigates Mr Cassidy’s background.
In episode two, the teenager’s family talk about how his death affected them and examines the police investigation, including a discussion with Detective Inspector Winters.
The third episode explores how the tragedy impacted on Mr Cassidy’s family and community and the remaining unanswered questions.
The documentary will be broadcast over three consecutive Saturdays, starting this week at January 16 on BBC Radio Ulster and will be available on BBC Sounds from this Saturday.