Nasser Qandil, a staunch defender of Syria's influence in Lebanon who surrendered on Tuesday at the request of UN investigators probing the 14 February killing, was released at 1.30am on Wednesday but refused to comment on the probe.
"I don't want to talk about this issue," Qandil said. "The information I gave [the investigators] belongs to the probe.
"I will only say that the cheap political and media exploitation is being done by some Lebanese parties and the [UN]commission has nothing to do with it," the former legislator said.
He was apparently referring to anti-Syrian groups who hailed the detention of former security chiefs for questioning in al-Hariri's killing.
The United Nations on Tuesday named Qandil and four pro-Syrian generals as suspects in the massive Beirut bombing that killed al-Hariri and 20 others.
The detentions were the first major break in the crime that transformed Lebanon.
Many Lebanese opposed to Syria's control over its smaller neighbour blamed Damascus and its Lebanese allies for the assassination. Both have denied the claims.
German prosecutor Detlev Mehlis
(L) is leading the UN investigation
The Lebanese government, acting at the request of the international body, detained three of the former Lebanese generals for questioning on Tuesday.
Major-General Jamil Sayyed, the former chief of General Security; Major-General Ali Hajj, the former director-general of the Internal Security Forces and Brigadier-General Raymond Azar, the former director-general of military intelligence, were detained at their homes.
A fourth, Presidential Guards Brigade commander Brigadier-General Mustafa Hamdan, surrendered for interrogation.
Qandil, who was in Syria when police went to his Beirut house, later returned by car and was escorted by two police vehicles from the Lebanese border to the capital.