Canadian investigators are in Paris today to take part in the long-awaited downloading of data from the flight recorders of the Ukrainian passenger jet shot down by Iran in January.

Canada's Transportation Safety Board confirmed today that after Tehran's nearly four-month delay, the so-called black boxes have arrived in Paris.

The TSB sent a team to Paris to witness the download of the data, after an Iranian news agency report that they had been shipped on Saturday.

Today marks a crucial step for grieving families seeking answers to why Iran's military fired two missiles at the passenger jet on Jan. 8 shortly after take-off from the Tehran airport.

All 176 people aboard were killed, including 55 Canadian citizens and 30 permanent residents and dozens of others with connections to Canada.

Iran initially denied responsibility but was forced to acknowledge the shootdown after video footage on social media appeared to show at least one missile striking the Boeing passenger jet.

The tragedy unfolded after Iran launched missiles into Iraq at two American military bases in retaliation for the U.S. having killed a top Iranian general.

Families of those who died on the plane have questioned why the plane was allowed to take off in such circumstances.