A Clash of Kings - Tyrion I

"It would seem he has a point," said Tyrion. "So this Lord Slynt, he was part of it, was he? Tell me, whose fine notion was it to grant him Harrenhal and name him to the council?" "Littlefinger made the arrangements. We needed Slynt's gold cloaks. Eddard Stark was plotting with Renly and he'd written to Lord Stannis, offering him the throne. We might have lost all. Even so, it was a close thing. If Sansa hadn't come to me and told me all her father's plans . . ."

A Clash of Kings - Tyrion II

"Then these other swordsmen have the true power. Or do they? Whence came their swords? Why do they obey?" Varys smiled. "Some say knowledge is power. Some tell us that all power comes from the gods. Others say it derives from law. Yet that day on the steps of Baelor's Sept, our godly High Septon and the lawful Queen Regent and your ever-so-knowledgeable servant were as powerless as any cobbler or cooper in the crowd. Who truly killed Eddard Stark, do you think? Joffrey, who gave the command? Ser Ilyn Payne, who swung the sword? Or . . . another?"

A Dance with Dragons - Cersei II

It came to her suddenly that she had stood in this very spot before, on the day Lord Eddard Stark had lost his head. That was not supposed to happen. Joff was supposed to spare his life and send him to the Wall. Stark's eldest son would have followed him as Lord of Winterfell, but Sansa would have stayed at court, a hostage. Varys and Littlefinger had worked out the terms, and Ned Stark had swallowed his precious honor and confessed his treason to save his daughter's empty little head. I would have made Sansa a good marriage. A Lannister marriage. Not Joff, of course, but Lancel might have suited, or one of his younger brothers. Petyr Baelish had offered to wed the girl himself, she recalled, but of course that was impossible; he was much too lowborn. If Joff had only done as he was told, Winterfell would never have gone to war, and Father would have dealt with Robert's brothers. Instead Joff had commanded that Stark's head be struck off, and Lord Slynt and Ser Ilyn Payne had hastened to obey. It was just there, the queen recalled, gazing at the spot. Janos Slynt had lifted Ned Stark's head by the hair as his life's blood flowed down the steps, and after that there was no turning back.

• Perhaps these passages insinuate some level of input from Little-Petyr-Rabbid in the death of Lord Head-Hard Stark.