The governor acted within the law, the attorney general said.
The inmates included Osaremwinda Aigbuohian and Daniel Nsofor, whose lawyers have been struggling to obtain a stay of execution on the death sentence; and two other convicts whose identities are yet to be ascertained.
Mr. Oshiomhole allegedly signed the death warrants of the unnamed duo last month, despite appeals by local and international organizations including Amnesty International and Access to Justice.
President Goodluck Jonathan had directed state governors to exercise their constitutional rights by signing death warrants of death row inmates in order to reduce the rising level of criminality in the country.
Henry Idahagbon, Edo State Attorney General and Commissioner for Justice, confirmed the development adding that the governor merely carried out his constitutional requirement by signing the warrants of the convicted criminals.
Mr. Idahagbon said that the defence team of the death row inmates, led by a civil society group, LEDAP, had tried up till the last minute to stop the hanging but did not succeed.
Three of the inmates were convicted outside Edo State and all the executed inmates had been issued the death penalty years ago, according to Mr. Idahagbon.
The Attorney General admitted that his office received petition papers for a stay of execution but could not do anything since the hanging had nothing to do with the state government.
It was gathered that notable Senior Advocates of Nigeria had backed the governor in the debate that followed his signing of the death warrant of Messrs Aigbuohian and Nsofor last September in exercise of his Prerogative of Mercy.
According to the Supreme Court, Mr. Aiguohian killed and dismembered the body of his victim while Mr. Nsofor forcefully robbed, tortured and strangulated his victim to death.
In Mr. Aiguohian’s statement of defence during trial, he described his action as a “mistake” but the Supreme Court in the affirmation of his death sentence in 2004 said, “the likes of Aiguohian belongs to Hades.”
The second convict, Nsofor, who also had his death sentence affirmed by the Supreme Court, was said to have strangled a woman to death after forcefully taking her money and torturing her.