Bush and Georgian President Mikhail Saakashvili were at a podium protected by the bulletproof barrier at a rally in Tbilisi in May when the grenade landed about 100 feet away. It did not explode, and investigators later said it apparently malfunctioned.
"I threw the grenade, not directly at where there was bulletproof glass, but toward the heads ... so that the shrapnel would fly behind the bulletproof glass," Vladimir Arutyunian said in the video broadcast by Georgia's Rustavi-2 television.
The station said the clip was provided by the Interior Ministry.
Arutyunian was arrested Wednesday after a shootout in which he was injured and a policeman was killed. He has been charged with murder in the policeman's death, but no charges have been filed in the May grenade incident.
Arutyunian has been in a hospital since his arrest. The video showed him lying propped up in his bed, but speaking lucidly and gesturing strongly.
Court officials on Saturday came to the hospital and ordered Arutyunian detained for three months while the investigation continues.
Investigators were searching for a motive. Suspicions that Arutyunian might be linked to Russian forces in Georgia followed reports that Russian military uniforms were found in his house after he was arrested.
But the deputy commander of Russia's forces in Georgia, Col. Vladimir Kuparadze, on Friday denied Arutyunian had any links to the Russian military. Russia has troops at two military bases in Georgia and their withdrawal, now scheduled for 2008, had been a tense issue between the two countries.
The Interior Ministry said Friday that Arutyunian was believed to have been a member of the Agordzineba party, which supported the leader of a region largely outside central government control.
Aslan Abashidze, the recalcitrant leader of the Adzharia region, fled to Russia last year amid street protests against his authoritarian rule.
The unrest erupted after Abashidze destroyed bridges linking Adzharia with the rest of Georgia and claimed that Saakashvili was preparing a military invasion.