German authorities are looking into whether to press charges against the gun-collecting father of the teenager who went on a shooting rampage at his former school on Wednesday, killing 15 people.
The motive for the attack by 17-year-old Tim Kretschmer remained unclear a day after the massacre in the southwestern town of Winnenden, reported Reuters.
The teenager, who neighbors described as a loner with a fondness for violent videos, appears to have taken his own life after police engaged him in a shootout hours after he fled the school and hijacked a car.
Kretschmer had taken a legally-registered 9-millimetre Beretta pistol owned by his father, a member of a shooting club.
Police said the father's other 14 guns were locked in a gun-closet as required by German law, but that he kept the Beretta in his bedroom.
"Everything here points to negligence on the part of the father as far as the storage of this weapon is concerned," said police spokesman Ralf Michelfelder.
He said it was now up to local prosecutors to decide whether to press charges against the father.
Germany toughened its gun laws in 2002 after 19-year-old Robert Steinhauser shot dead 16 people, mainly teachers, and himself at a high school in the eastern German city of Erfurt.
The changes raised the minimum age for gun ownership to 21 from 18 and required gun buyers under 25 to present a certificate of medical and psychological health.
German gun control laws already required applicants to pass rigorous exams that can take up to a year, but there are close to eight million legally held weapons in the country, roughly one for every 10 people.
Schools were closed in Winnenden on Thursday but students streamed to the Albertville Realschule, scene of the shootings, with flowers, candles, CDs and stuffed animals. Some stood in silent grief, some cried and some clung to friends or parents.
Police said on Thursday Kretschmer had fired 60 rounds in the school after entering a classroom at around 9.30 a.m. (0830 GMT). He shot many of his victims in the head at close range and appears to have targeted women.
Eight of the nine students and all three of the teachers he killed in the school were female.
When police arrived at the school Kretschmer fled, shot another person in front of a nearby psychiatric clinic and then forced a motorist to drive him out of Winnenden, a town of 27,000 near Stuttgart.
He jumped out of the hijacked car in Wendlingen, some 30 km (20 miles) from the school, shot two men at a car dealership and severely injured two policemen before apparently turning the gun on himself.