On the most recent "General Hospital" episode, Ava Jerome received another photo along with a note that read simply: "Don't tell anyone." She explained what was happening to Nina Reeves (Cynthia Watros) and argued that Cyrus Renault couldn't be behind it because he knows she would just involve Sonny. Such mind games are more in Nikolas Cassadine's wheelhouse. Plus, he likely wants to get revenge on her, and framing Ava for Dr. Austin Gatlin-Holt's death would be the perfect way to do it. Moreover, Cyrus is too obvious a candidate. 

However, the stalker being revealed as Nikolas would also be slightly predictable. Ava suggested that Nik wouldn't risk being seen in Port Charles and perhaps had someone else plant the notes for him. After saying goodbye to Nina, Ava found a slightly open drawer in her desk that contained a gun and another note that read: "You never know when you'll need it." One radical theory posed by a fan on X, formerly Twitter, was, "I am 100% sure Nikolas didn't kill Austin. But I have a nagging suspicion that Ryan isn't dead, and he killed Austin for Ava just like he did w [Kiki]." 

Serial killer Ryan Chamberlain (Jon Lindstrom) became obsessed with Ava but he was killed by police detective Dante Falconeri (Dominic Zamprogna) back in February. He previously swapped places with his good twin, Kevin Collins, and Ava almost married the man who killed her daughter, Kiki Jerome (Hayley Erin), as a result. Having him turn out to be Ava's stalker might be a reach, but it would definitely be a thrilling development!