BERLIN (AP) — German police released an initial description Wednesday of a suspect wanted in connection with a knife attack at a gym in the western city of Duisburg that left four men seriously wounded.

Police said witnesses interviewed after the attack late Tuesday described the man as being about 30 years old, 180cm (5 feet 11 inches) tall, of normal build and with a long black beard. They added that witnesses said he had a “southern” appearance — a term sometimes used in Germany to describe people of Mediterranean origin — and wore a long-sleeved pullover, dark trousers and a black baseball cap.

Investigators were still looking into a possible motive, however it appeared that it was not an indiscriminate attack, said Herbert Reul, the state interior minister of North Rhine-Westphalia, where Duisburg is located. He did not elaborate.

“I hope that the victims will recover quickly and that everyone who was on the scene and saw this terrible act will recover,” Reul added.

Prosecutor Jill McCuller said later that it appeared one or more of the victims had had an altercation with the attacker, German news agency dpa reported. She said investigators were still trying to clarify whether the attacker was also a member of the gym.

Police said the four victims are German citizens aged 21 and 32, and two aged 24. The 21-year-old victim remains in a life-threatening condition and may have to undergo a second surgery, McCuller said. Officers were not yet able to interview any of the victims, meaning the description of the attacker couldn’t yet be verified.

McCuller said there were no surveillance cameras in the gym making it difficult to reconstruct the exact course of the attack.

Authorities have asked members of the public with any information about the attack to get in touch and submit relevant photos or videos.

Police said a “stabbing or cutting weapon” was used in the attack at the gym, which is part of the John Reed Fitness chain.

The company said in a statement that it deeply regretted the incident and expressed hope that the victims would recover quickly.

Last month, a gunman stormed a service at his former Jehovah’s Witness hall in the northern Germany city of Hamburg, killing six people before taking his own life after police arrived.