I kinda thought it was bad writting when after Chrissy was dead they said they found cocaine in his system, when heroin was clearly his drug of choice..
and he was also nodding out at the wheel which showed he was high on H (good acting by the way) and Tony noticed that. and you could see the shame in his eyes right before the accident. he knew Chrissy would never be what he wanted him to be.
I think Tony killing Chrissy was the most disturbing moment I have ever wittnessed on film. I had to stop it at first and take 15 before finally finishing that episode..wow!

for the folks who feel Tony shouldn't have killed Chrissy must have been missing something.(although it did catch me by surprise!) because the build up was very obvious...