Winnenden, Germany - Police said Monday they had launched a criminal investigation into the father of a teenager who went on a killing spree at school in south-west Germany last week.

Investigators were trying to determine whether the man should answer charges of causing death through negligence, a police spokeswoman told Deutsche Presse-Agentur dpa.

The father of gunman Thomas Kretschmer, 17, has been described as a passionate marksman who kept 15 weapons and 4,600 rounds of ammunition at his home.

All the weapons were locked in a safe except for the Beretta pistol used by his son to kill 12 students and teachers at the Albertville Secondary School in Winnenden on March 11.

The teenager, a former pupil at the school, shot dead three other people as he fled the town, before police stopped him and he turned the gun on himself.

Kretschmer fired more than 100 shoots in his rampage from the handgun he stole from his father's bedroom.

Some of the pupils at the school resumed classes on Monday. More than 150 boys and girls were taken by bus to six community halls in the area where they were cared for by teachers and psychologists.

Officials said they had not decided whether to reopen the school and were considering plans to move classes to other schools so the traumatized pupils would not have to remain solely among themselves.

A funeral was due to be held Monday for one of the female pupils killed in the attack. Further funerals are due to take place during the week. The first victim, a 16-year-old girl, was buried Saturday.

Two girls and two policemen injured by Kretschmer remained in hospital Monday, but were said to be out of danger.

Lessons at a school in the southern town of Freiburg were cancelled on Monday, following a warning that someone planned to run amok. Another school in the town was evacuated on Friday after a similar threat.

Police continued to delve into the motives for the attack. News reports said the teenager had been playing violent internet video games the previous night.

It remained unclear whether Kretschmer had previously undergone psychological treatment, as had initially been reported by police.

The boy's parents denied their son had ever had psychological therapy, but officials said he had been to a hospital outpatients department of diagnostic tests.

The Winnenden shooting was Germany's worst school bloodbath since April 2002, when a 19-year-old high school student went on a rampage in Erfurt, killing 16 people before taking his own life. (dpa)