Witnesses have been unable to confirm suspicions that the mortar exploded as a result of double loading.
Some witnesses claimed that a round was being loaded into the mortar before it had discharged a previous one. Other witnesses were not so sure.
The police laboratory in Vantaa is currently investigating whether it can find traces of two shells from evidence gathered at the site of the accident.
The accident investigation board met on Tuesday for the first time to review the results of their probe.
An interim report will be published in late spring. A final report is expected next summer, when the board will also release a list of recommendations to the defence forces to improve safety in live-fire exercises.
The explosion killed one conscript and injured six others.