It was in reality a horrific period of their lives. Your parents passed through personally. Many families where totally wiped out. I found it signifigant that at least most of the immediate family where not.

It never has really stopped unfortunatly. Women and children are still being killed. People wear blinders to situations. Mans inhumanity to others has always disturbed me.

If you speak German or have an acquaintance who does. If your father has not searched extensively. Or if your father has the name of that engineer that was good to him.I suspect he still has.

Some effort could be taken on to find his fate. Or even if he just survived the immediate period. I imagine all engineers where registered at the time. Perhaps your father did at some point. Although it might be worth a probe again with the internet of today. I am certain your father would appreciate it.