Castiel and Uriel had dean torture the same person that tortured him, Alastair...

the two angels had dean torture Alastair to get info of who's killing the angels,seven angels had died.

Alastair had made dean torture and kill others in hell,dean had been broken in for 30 hell years,but six months in human years. Dean had been one of the best tortures in hell .

at the end of the way, Alastair broke free due to water from a pipe washing away the devil's trap and he beat the shit out of dean landing him in the hospital.

And then Castiel had found out who did it,only an angel can kill another angel, Uriel killed the people who refused to join his side,and Castiel killed him.

After cas had taken care of Uriel he had went to the hospital. at the hospital when dean asked if he started everything from Lilith to what happened ,because of Alastair saying he had broken the first seal.

Castiel confirmed, dean's heart went to his feet, quietly a tear ran down deans face,in the hospital as he knew this was his fault because he took up torturing souls...

'And it is written, that the first Seal shall be broken when a Righteous Man sheds blood in Hell. As he breaks, so shall it break...'