Mourners gather on Thursday morning in front of the Albertville school in Winnenden, Germany, where a gunman killed nine students and three teachers the day before. ((Michael Probst/Associated Press))

German police now say they doubt the credibility of a chat room post attributed to a teenager who went on a shooting rampage.

Authorities are investigating whether the internet posting was faked, police spokesman Klaus Hinderer said.

Tim Kretschmer's computer showed no trace of his having made the posting in a chat room conversation, he added.

Hinderer's statement Thursday contradicts his earlier announcement that authorities were "completely convinced of the veracity of the post."

The post appeared in a chat room about six hours before Kretschmer went on a rampage Wednesday at Albertville technical high school in Winnenden, northeast of Stuttgart, killing nine people and three teachers, said regional police Chief Erwin Hetger.

He then shot and killed three more people at another location before killing himself.

Memorials at school

The high school remained cordoned off by police tape on Thursday as authorities continued to examine the scene inside, where at least 60 shell casings had been found.

Students, parents and staff gathered outside the school as the community of 28,000 mourned the victims.

Flags outside the school flew at half-mast while flowers, candles and placards — some asking "Why?" — were placed around the building.

The gunman, dressed in black combat gear, entered the school of about 1,000 on Wednesday at 9:30 a.m. Soon after entering the facility, he opened fire in two classrooms, killing eight girls, one boy and three teachers with a Beretta 9-mm pistol that was reportedly taken from its unsecured hiding spot in his parents' bedroom.

The principal warned teachers of the attack using a coded emergency message that was established as part of a national emergency alert system after a deadly school shooting in Erfurt in 2002.

The principal stated "Frau Koma is coming" on the school's public administration system and teachers then closed their classroom doors and windows and ordered students to sit on the floor.

Hetger said when police arrived, they entered the building in small teams and the gunman fired shots at them before fleeing.

The teenager then fled the school, shooting one pedestrian to death before hijacking a car and forcing the driver to take him to Wendlingen, about 40 kilometres away.

With the police in pursuit, the teenager fled on foot to a car dealership in the town, where he shot and killed a salesman and customer before engaging in a gun battle with police.

He ran down a dead-end street where police said he was found dead with an apparently self-inflicted gunshot wound to the head.

Suspect a quiet loner


Students light candles in front of the Albertville school in Winnenden, Germany, on Thursday. ((Thomas Kienzle/Associated Press))

Police have only identified the gunman as Tim K. Authorities said the teen was a below-average student while attending Albertville, but graduated last year.

The gunman's younger sister still attends the school.

Friends and acquaintances have told local media that Kretschmer was a quiet loner who wore glasses and enjoyed practising in a shooting range with pellet guns, competing in local table tennis tournaments, playing video games and playing poker and chatting online.

The teen had reportedly begun a salesman apprenticeship while studying at a private business school he had entered after finishing high school.

Authorities have not released any details regarding the gunman's possible motive for the shooting. Most of the victims were teenaged girls. Three female teachers were also killed. Only one male student was killed in the attack and three men were shot after the teen fled the scene.

Police said no written communication has yet been found that provides an indication of what may have provoked the attack.

Investigator Siegfried Mahler said Thursday that authorities had learned that the suspect was treated for depression in 2008.

With files from the Associated Press