David Heiss,, told a court Wednesday that he was frustrated at being blocked from Warcentral.com, the Advance Wars online forum run by victim Matthew Pyke and his girlfriend Joanna Witton.
Heiss is accused of flying from his home in Germany to Nottingham in the U.K. and murdering Pyke, who died from 86 stab wounds.
The court heard Tuesday that Pyke had tried to write the killer's name on his computer with his own blood.
Heiss was allegedly obsessed with Witton. In a conversation with another member of Warcentral.com, Heiss allegedly said that he hated having to blackmail her, but that seemed like the only way he could talk to her.
Questioned by the prosecution as to what he was blackmailing her with, Heiss replied: "At some point I said if they didn't try to resolve this, then I would come back."
The prosecutor pressed Heiss as to whether he meant he would come back to Nottingham if he wasn't unblocked. "Unfortunately, yes," said Heiss.
He added: "At some point I simply couldn't think of anything else to persuade them to talk to me other than to blackmail them."
The jury was also told that Witton had asked Heiss on his of his previous surprise visits to get over her and seek counseling.
The case continues.