|Mr Putin celebrated Victory Day last year with a military parade in Sevastopol|
Mr Putin said on TV he had ordered work on "returning Crimea" to begin at an all-night meeting on 22 February.
The meeting was called after Ukrainian President Viktor Yanukovych was ousted.
Speaking last year, Mr Putin had said only that he took his final decision about Crimea after secret, undated opinion polls showed 80% of Crimeans favoured joining Russia.
The findings of these polls were borne out by the outcome of the referendum on 16 March, he told Russian state TV last April.
"I invited the leaders of our special services and the defence ministry to the Kremlin and set them the task of saving the life of the president of Ukraine, who would simply have been liquidated," he said.
"We finished about seven in the morning. When we were parting, I told all my colleagues, 'We are forced to begin the work to bring Crimea back into Russia'."
|Armed man at Simferopol airport|
"Little green men" appeared in Crimea before the referendum
On 27 February, unidentified armed men seized the local parliament and local government buildings in Crimea, raising the Russian flag.
Among them appeared to be regular soldiers without military insignia, who were dubbed the "little green men".
Mr Putin subsequently admitted deploying troops on the peninsula to "stand behind Crimea's self-defence forces".
Timeline: How Crimea was annexed
22 February, former Ukrainian President Viktor Yanukovych flees Kiev after violent protests
23 February, Russian President Vladimir Putin plans to rescue Mr Yanukovych and annexe Crimea
27 February, pro-Russian gunmen seize Crimea's parliament and other key buildings
28 February, unidentified soldiers in combat fatigues occupy two airports in Crimea
1 March, Russian parliament approves Mr Putin's request to use force in Ukraine
16 March, 97% of voters in Crimea agree to join Russia
18 March, Mr Putin signs a bill absorbing Crimea into the Russian Federation
The formal annexation of Crimea sparked unrest in eastern Ukraine on 7 April, when pro-Russian protesters occupied government buildings in Donetsk, Luhansk and Kharkiv demanding independence.
A month later, pro-Russian separatists in Donetsk and Luhansk declared independence from Ukraine after unrecognised referendums.
Ukraine responded by launching an "anti-terrorist operation" against them and the region became engulfed in a conflict which has cost at least 6,000 lives and driven more than a million people from their homes, according to the UN.
The Ukrainian government, Western leaders and Nato say there is clear evidence that Russia is helping the separatists with heavy weapons and soldiers. Independent experts echo that accusation.
Moscow denies it, insisting that any Russians serving with the rebels are "volunteers".
Full details of Mr Yanukovych's escape from Ukraine are unclear although Mr Putin spoke of preparations to evacuate him from Donetsk.
"Heavy machine guns were placed there, so as not to waste time talking," he added, with preparations made by land, sea and air.
The documentary, which Russian TV says will be broadcast soon, was made by Andrei Kondrashov, a journalist with state-run channel Rossiya-1.
So with the pull-back of heavy equipment by eastern Ukraine rebels announced today and the admission by Putin that the little green men were actually Russian soldiers, as if everyone in the world didn't know, could it be that Putin is not going to pursue the annexation of eastern Ukraine? It seems an odd time to make such an admission if he was still on the mission of annexing another chunk of Ukraine. Maybe he's had enough of the sanctions.