According to the paper, the grenade was discovered by the police after the incident.
An eyewitness told Bild that the attacker was speaking in “broken German language.”
The police said that they currently have no leads linking the man to radical Islam, and other motives are being looked into.
A masked man entered the cinema at midday on Thursday. According to initial reports, he was carrying a rifle and had cartridge belt around his shoulder.
Cinema employee Guri Blakaj told Reuters the gunman, who appeared to be aged between 18 and 25, told workers to get into an office.
The attacker then went into one of the cinemas from where the shots were reported.
"I realized that something had happened. I called the police and ordered the staff to leave the house immediately,” one of the managers at the cinema was cited as saying by Bild.
One of the hostages, Almir H., 16, told the paper that the gunman ordered them to lie down on the floor in the toilet, threatening to shoot if the hostages didn’t obey his command.
When he ran out of the restroom “there were apparently four shots, but I do not know whether that is true,” he said.
Initial reports claimed that 20 to 50 people were injured in the incident. But police later said that all hostages were released unharmed after the perpetrator was neutralized.