I don't think he deserved to go to prison - it was clearly an accident. He wasn't speeding, and he wasn't drunk or under the influence, it seems that he instinctively started driving on the side of the road that Americans drive on normally, which is a horrible mistake but definitely not deliberate. It was also raining that day which meant that the car could have skidded into the wrong lane by accident as well.

And as for "forgetting the incident" it's not that he denies it happened, but because he was seriously injured in the crash too, he didn't remember the accident itself, only waking up in hospital afterwards.

While understandably the victims' families were very upset that he only got a small fine, later on one of the family members came out and said that he forgave Broderick because he knows it "wasn't deliberate".

It was a terrible tragedy and clearly something that Broderick should regret for the rest of his life. But I don't think it's on the same kind of level as "driving drunk, or deliberately speeding" which would rightfully get a vehicular manslaughter charge.