Basit Balahim, alias Leklek Tuballa, 16, said the blindfolded Sobero cried, "No, no, please, I beg you!" as he was told to kneel on the rocky ground with his hands tied behind his back.
Basit smiled as he described the gruesome murder to reporters in detail.
Ignoring his fathers shouts for him to be quiet, Basit, surrounded by police, related how Sobero pleaded for his life as the executioner, Abu Sayyaf member Abu Haija, prepared to chop his head off with a machete.
Zamboanga police director Senior Superintendent Daming Unga said Basit and his father, Abdulkab Balahim, 48, were captured in Tuburan town, Basilan last week, along with two other suspected Abu Sayyaf bandits.
Unga said the Balahims and Commander Faizal Abbas each carried a P1-million bounty on their heads, while a fourth suspect was still being interrogated by military intelligence agents.
"We are positive that the (fourth suspect) is one of those who participated in the raid on Dos Palmas in Palawan," he said.
Basit, Abdulkab, Abbas and the other suspected Abu Sayyaf bandits are detained at the headquarters of Mindanao Task Force in Zamboanga City.
Soberos scattered bones were found in the jungle between Tipo-Tipo and Lamitan towns in Basilan earlier this month by government troops and later turned over to the United States Embassy in Manila for identification.
Two weeks ago, the US government announced that forensic experts from the Federal Bureau of Investigation (FBI) in Honolulu, Hawaii established the remains were indeed Soberos.
Last June, Abu Sayyaf spokesman Abu Sabaya told reporters they beheaded Sobero to warn the military to halt the offensive against them.
Sobero, along with American missionary couple Martin and Gracia Burnham and dozens of Filipinos, was snatched by Abu Sayyaf bandits from the Dos Palmas resort in Palawan last May.
Meanwhile, the military said a captured Abu Sayyaf bandit who offered to lead government troops to the Burnhams was killed Tuesday when he grabbed a grenade from a soldier in an escape attempt.
Bachong Ladja, who was captured in Basilan last week, blew himself up when the grenade went off in his hand, the military added.
The soldiers were following him through the jungle when Ladja grabbed a grenade from a trooper, regional military operations chief Col. Roland Detabali said.
Detabali said the soldier was able to push Ladja away before he could throw the grenade and it went off his hand, killing him and wounding the soldier. With wire reports