According to police, his rivals Madhush of Makandura and Angoda Lokka had got together to plan the murder.
An attempt by the latter on Samayan’s life previously, on 23 October 2015 at Kaduwela courts, failed.
But, he did not escape a week ago.
Coming to know about another attempt to kill Samayan, police strengthened security in the Kaduwela court and its vicinity.
However, evading their eye, the killers, former soldiers with special experience, chose an isolated location with two hillocks by the roadside around 200 metres away from Malwatte prison in Kalutara.
Eleven prison officers escorted Samayan and five other detainees in two prison buses, sans the regular police protection.
Before they entered the highway, a cab blocked their path at Ethanamadala and the gunmen wearing police-like uniforms got to work.
Some stormed the prison bus and found their target, shot him and dragged him to the foot-board of the bus.
All this took a few minutes to happen.
The gunmen did not allow the prison officers to use their five T-56 weapons, excepting one.
But, officer Sannigam did not last long with his gun and died in a pool of blood.
So did jailor Wijeratne, while five other officers sustained injuries.
The assailants abandoned their cab and got away in a Dolphin van.
Investigators say around 10 gunmen, including Angoda Lokka and Athurugiriye Ladiya had taken part in the attack.
Police later found the van, which had been hijacked from Maradana, abandoned in Morahahena.
Airports have been alerted about possible attempts by the killers to flee the country.