Final answer:
The texts provided do not mention a character named Matt or Strout or their circumstances, instead focusing on Lassiter and his experiences with violence and morality.
Step-by-step explanation:
Who helped Matt kill Strout? The given texts do not explicitly identify a character named Matt or detail the circumstances around a character named Strout being killed. The excerpts provided focus on Lassiter, a character who is entreated by a woman to give up his guns to prevent further killing, and on another occasion deliberately shoots to cripple but not to kill. These narratives revolve around themes of redemption, morality, and the impact of violence, as well as the complex relationships between the characters, rather than the act of helping someone named Matt kill a character named Strout.