"It makes me feel very bad, because it makes me feel sad to think everything I always did for him when the school was open," said Jonas.
Jonas has since erased the voice message from his phone, a standard message when students do not show up at school.
The Department of Education, and even the mayor have expressed regret for the phone call, but Jonas said that more than an apology, he wants the teachers involved to take responsibility for the death of his son.
The reminder was enough to lead Jonas to show Eyewitness News the clothing Jean Fritz wore before he, and one other student jumped into Hessian Lake, where swimming is not allowed.
According to Jonas, the teacher did not say "don't go in the water", and instead just wanted to know who was swimming.
Jonas says he does not at all blame the teachers. As for the troubling phone call?
"Everybody came to the funeral? Why'd you call me?" he adds.
Jonas says he has not ruled out a lawsuit over his son's death.