Focus on Gunman's Father

German police said Monday the father, who legally kept more than a dozen guns at his house and 4,600 rounds of ammunition, was under investigation on suspicion of causing death through negligence.

All the weapons except one, a 9mm Beretta pistol, were said to be locked in a safe at the residence. The teenage gunman Tim K is believed to have stolen the unsecured pistol from his father's bedroom and used it to shoot dead 12 students and teachers at the Albertville Secondary School on March 11.

Prosecutors could charge the man, whose name has not been released, with involuntary manslaughter for leaving the murder weapons unlocked in his bedroom despite knowing his son was depressed.

Police have said that Tim K was treated for depression between April and September of last year, before breaking off his treatment.

"There are concrete signs that the parents knew of their son's health problems," the prosecutors and local police said in a joint statement. "Based on this, there is reason to suspect this may be a case of involuntary manslaughter."

Motives remain a mystery

The teenager, a former pupil at the school where he went on a shooting rampage, killed three other people as he fled the town, before police stopped him and he turned the gun on himself.

A funeral was due to be held Monday for one of the female pupils killed in the attack. Further funerals are to take place during the week.

Two female students and two policemen injured by Tim K remained in hospital Monday, but were said to be in stable conditions.

Police said they were still investigating motives for the attack.

The Winnenden tragedy was Germany's worst school shooting 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.