He just needs to prove it. 

"M-My Father," Xia Sha couldn't speak properly. 

Ruan Jing Tian nods his head vigorously. He is sure that the ring Xia Sha found on Yan Xi's house belongs to Mr.Xia Qi Feng and Mrs. Xia. No wonder it felt so familiar. 

Xia Sha frowned. Although the ring is somewhat familiar in her eyes, she couldn't fathom why Yan Xi had it. While Yan Xi is her distant cousin, Xia Qi Feng never cares enough to visit Yan Xi's apartment. 

Therefore, the ring shouldn't end up in Yan Xi's apartment. 

The only rational reason that crossed her might right now is-

"Do you remember that you forced me to steal the wedding ring the night before your father's wedding?" Ruan Jing Tian asked seriously.

Xia Sha has vague memories of forcing Ruan Jing Tian to commit a criminal act. 

Author and Ruan Jing Tian: "Déjà vu?"