Ethan Landry is the murderer of Sutton Mercer and Nisha. It is revealed that he was so in love with Sutton that he would do anything for her such as trying to find her birth mother. He killed her out of rejection.
Ethan is an odd character in the series. It is revealed that he killed a girl when he was 10 years old, and though it was first passed off as an accident, but he eventually admits that he killed her because she was playing with another kid in the neighborhood. This is very similar to the reason he killed Sutton ( out of jealousy ). He is known to be mysterious and loves writing poetry. He loves science and had his chance of a scholarship ruined by Sutton. It was known in Hide and Seek that he did indeed have feelings for Sutton, as he told Emma that he overheard Sutton saying in the halls of school that she loved playing night games. She said that it was really sexy playing under the stars. This stuck with him. This shows that he watched her a lot and always listened to what she said. He paid a lot of attention to her and always knew everything that she said or what was going on with her life. Ethan was later arrested for both of the murders that he committed.
Ethan was obsessed with Sutton, up to the point that he wanted to find Sutton's birth-mother. Instead, he found Emma and went briefly to Las Vegas to stalk Emma. That night, after Sutton's conversation with Garett (Garett arrived after Becky left. Sutton did something horrible to Garett's sister), Ethan came and kissed Sutton but Sutton rejected him so he killed her. Ethan lured Emma to Phoenix by sending the video (which shows someone strangling Sutton) to Travis and hacked Sutton's Facebook account. By the way, he got the video from Laurel's laptop. He hacked the alarm code in Char's and Nisha's house so he can get in. He ran Thayer over that night because he was jealous of Thayer's relationship with Sutton. He was good at hacking things so anything was possible for him.
He never meant to fall for Emma but he did. That's why he kept on suggesting someone capable of doing murder so Emma would be blindsided to who the real killer was. When Ethan found out that Nisha has his medical report, he overdosed Nisha's drinking water with Valium causing her to fall on the pool and die.