Victims of a shopping centre shooting that left six people dead are suing the gunman’s parents, claiming they failed to act on signs that his mental health was failing.

Six people died and 17 others were injured when Tristan van der Vlis opened fire in the Ridderhof mall in Alphen aan den Rijn in April 2011, before taking his own life. Lawyers said 13 victims and their families were involved in the compensation claim.

AD reported that Van der Vlis’s mother had admitted in an earlier hearing that her son was depressed and had talked to spirits of dead people. She added she was surprised that Tristan had been granted a gun owner’s licence.

The 24-year-old had also shown signs of unusual behaviour at the warehouse where he worked. Lawyer Lionel Lalji, who is representing the families, said he wanted to establish responsibility so his clients could receive compensation from the relevant insurers.

Adem Aksoy, who was wounded in the Ridderhof shooting, told AD: ‘Everyone has passed the question of responsibility onto someone else because they’re worried about compensation claims. Nobody has apologised. That’s what I want so I can close the issue.’

A hearing in the compensation case is scheduled for March 6.