Joshua Parkes, Lucy Tibbetts and Isabelle Floyd died after a Skodia Fabia crashed into a tree in Bromley Lane on October 13.
Nathan Cartwright died on Saturday from his injuries, while a 16-year-old girl remains in hospital in a critical but stable condition.
The IOPC said it would examine the level of involvement West Midlands Police had before the crash.
Investigators from the IOPC said the Skoda had come to the attention of a marked police vehicle before the crash, with the issue referred to them by the force.
West Midlands Police, which is conducting its own investigation, said the police car wasn't in the "immediate vicinity" of the Skoda at the point of collision.
IOPC regional director for the West Midlands, Derrick Campbell, said: "Our sympathies are with the families and everyone else affected by this tragic incident.
"It is our role to provide the independent scrutiny which is necessary in these circumstances and we will establish the facts. In the meantime, we acknowledge concerns in the community but would stress that speculation is not helpful to anyone.
"The evidence we have gathered so far indicates there was no direct contact between the police vehicle and the Skoda, but our inquiries will look at whether there was any other form of interaction between them prior to the collision.
"We have made contact with the families of those involved to explain our role and we will keep them regularly updated as our investigation progresses."
Investigators from the independent body attended the scene with an assessment carried out after being notified by police. In-car data from the police car and CCTV footage has been gathered for review.