Death is so final…
If you throw them in jail for life, and 30 years later some new light is shed on the situation and the guy turns out to be innocent (e.g. DNA forensics), you can let them out. But then again you could argue that locking up someone for 30 years and then saying “oh sorry, we made a mistake, you can come out now” is just as damaging or more.
On the other hand, you simply can’t revive a dead person. Ever. No matter how long or short it’s been since they died. At least there’s some hope for inprisonment.