Klaus wanted to trust Ansel and his intent to reunite with his son, but he felt obligated to kill him to ensure Hope's safety, as he knew that if Ansel continued to live with the knowledge that Hope was alive, Esther would eventually find out and use that information to try to hurt her once again.

Does Klaus ever meet Ansel?

Niklaus Mikaelson

Klaus first met Ansel when he found the father's deceased body impaled. ... Klaus clearly wanted to get to know Ansel and spend his time with him as a true son, but once Ansel revealed that he knew that Hope Mikaelson was still alive, Klaus was forced to end Ansel's life.

Why does Klaus pretend to kill Aiden?

Just as Dahlia intended, Aiden's body was found by Josh and Davina, who immediately contacted Jackson about it. Jackson then brought his body to the safe house, where he immediately accused Klaus of killing Aiden in retribution for exposing his plan earlier.