One day after the knife attack on two controllers in an S-Bahn at Gateway Gardens station, the background to the crime is still unclear.
The investigators are hoping for information about the course of events from video recordings that show what is happening around the attack.
A police spokesman said on Thursday.
According to current knowledge, the two railway employees had informed the man of the mask requirement, which still applies in local public transport.
The 27-year-old Somali also did not have a ticket.
When the situation escalated and the man attacked the inspectors, the police were called.
An officer finally shot the attacker in the leg with a well-aimed shot.
The attacker is currently in the hospital with serious but non-life-threatening injuries.
The inspectors were taken to a clinic with cuts but have since been released, it said.
The police did not say on Thursday what exactly can be seen on the video recordings.
She also evaluates traces from the crime scene, as a spokesman said.
As is usual in such cases, investigations were also launched against the officer who fired the shot.