A terror suspect shot dead after he stabbed two Australian counterterrorism police officers may not have been acting alone as originally thought, a lead investigator said Thursday.

Numan Haider, 18, was killed Tuesday after he stabbed two officers during a meeting outside a Melbourne police station. Police initially said Haider appeared to be working on his own, but Victoria Police Chief Commissioner Ken Lay said new information suggests that might not be the case.

"There's some information that he was certainly talking to other people around the time that he came to the police station," Lay told Australian Broadcasting Corp. "It's just a little unclear to us at the moment whether there were actually people at the police station with him, whether they dropped him off, whether they were waiting for him."

Haider caught authorities' attention about three months ago, after police say he began displaying a series of troubling behaviors, including waving what appeared to be an Islamic State flag at a shopping center. His passport was canceled about a week ago on national security grounds.

Lay said police visited Haider's home earlier Tuesday to set up the meeting. When the three met outside the station Tuesday night, they exchanged handshakes before Haider began stabbing the officers. Police say one of the officers then fired at Haider, killing him. A second knife was later found on Haider's body, police said.

The Victorian police officer who was stabbed was expected to leave the hospital on Thursday, Justice Minister Michael Keenan told Parliament. The federal police officer, who received the most severe injuries, remained hospitalized but was doing well, Keenan said.

Some experts suspect the attack was inspired by the Islamic State group's recent call to supporters to wage terrorism in their home countries.

In an address to the United Nations on foreign fighters, Prime Minister Tony Abbott blamed Islamic State for the attack, describing the group as a "death cult" that had "declared war on the world."

"It's hard to image that citizens of a pluralist democracy could have succumbed to such delusions, yet clearly they have," Abbott said.

Earlier this month, Australia raised its terror warning to the second-highest level, citing the domestic threat posed by Islamic State supporters. Last week, police detained 16 people in counterterrorism raids in Sydney and charged one with conspiring with an Islamic State leader in Syria to behead a random person.