The Northern Ireland Police Ombudsman is appealing for witnesses after a teenage girl was knocked down and killed following a night out.
Shannon McQuillan, 19, died when she was struck by a van near Toomebridge, Co Antrim, during the early hours of Saturday.
Her 21-year-old boyfriend, Owen McFerran, who was also struck, remains in a critical condition in Belfast's Royal Victoria Hospital.
The couple had been in contact with police and ambulance crews before the crash.
The police watchdog confirmed investigators were examining police actions during the events leading up to the fatal crash on Moneynick Road at about 3.40am on Saturday.
A spokesman said: "We would wish to express our sincere condolences to Shannon's family on their tragic and untimely loss.
"Our thoughts are also with Owen's family and friends at this very difficult time.
"Our investigators are now working to establish what happened during the interaction between police officers and Shannon and Owen prior to the collision."
It is understood Ms McQuillan had fallen on ice in Magherafelt a short time earlier.
An ambulance was called at about 2am as she was found to be unresponsive, however, the journey to hospital was terminated on the outskirts of Toome.
The Ombudsman's Office spokesman added: "As part of routine police patrolling, officers were in the area of Secrets Nightclub in Magherafelt in the early hours of Saturday morning.
"Between 1.30am and 2am Shannon slipped on ice and required medical assistance. An ambulance was requested.
"Officers were then called to an incident on the Moneynick Road, near Toome, at around 2.50am, as a result of which there was further contact between police and Shannon and Owen."
Ms McQuillan, from Dunloy, was in her second year at Ulster University studying law and criminology.
Students from the university's law society were among those to pay tribute on social media.
A funeral mass is due to take place at St Joseph's Church in Dunloy at 11am on Wednesday.
Parish priest Fr Liam Blaney, who has been comforting the family, described the teenager as a talented, lively and personable young woman.
Her heartbroken family were being supported by the close-knit rural community, he added.
Fr Blayney said: "They are grief-stricken, naturally enough, given the sudden and unexpected nature of her death in a very confused set of circumstances.
"They are finding it very difficult. It is hard for the whole family but there is a very supportive community living nearby.
"They are a very well-known family and there would be a large extended family in the area who have all rallied round."
The Police Service of Northern Ireland (PSNI) said they notified the Ombudsman's of the incident, following normal, established protocol.
The Northern Ireland Ambulance Service (NIAS) has also launched a separate internal investigation.
Meanwhile, Sinn Fein MLA Philip McGuigan, who also knows the family, said they were keen to establish exactly what happened.
He said: "The family are determined that we get all the facts of what happened on the night and I fully support them in this endeavour.
"Obviously the additional information has compounded an already grief-stricken family."
Anyone with information is asked to call the freephone witness appeal on 0800 032 7880.