Bad Parents or just plain stupid?

I could relate to this kind of parents. I have read a news from the Internet of drug addict parents. They had left their mixture of drugs place in baby's drinking glass on the table.

Beyond their notice, their 2-year old daughter grabbed her drinking glass and engulfed the content. The baby died instantly. So what the parents can do is to be sorry? Sorry for their stupidity? Sorry for their irresponsibility?