A team of 18 Russian investigators has arrived in Turkey to establish what led to the assassination of the Russian ambassador in Ankara, Andrei Karlov.
Mr Karlov was shot by Mevlut Mert Altintas, 22, apparently in protest at Russia's involvement in Aleppo, nine times as he gave a speech on Monday.
Police have arrested six people over the killing, including Altintas's mother, father, sister and three other relatives, as well as his roommate.
Mr Karlov's body is being flown back to Russia and on Tuesday afternoon his coffin was carried across Esenboga airport's tarmac, draped in a Russian flag.
He was accompanied to a waiting plane, sent by Moscow, by an honour guard of six Turkish soldiers.
A short ceremony, attended by Ankara's top diplomats and Turkey's Deputy Prime Minister Tugrul Turkes, took place before Karlov left the country for the last time.
In highly unusual scenes for a Muslim country, a Russian Orthodox priest said prayers and swung incense over the coffin, while a Turkish soldier stood holding a picture of the murdered diplomat and Mr Karlov's widow Marina wept.
Mrs Karlov was present when Altintas opened fire on her husband, who took up his posting in Ankara in 2013.
It was not clear if the gunman, an Ankara riot police member who was later shot dead in a gun fight with Turkish officers, had links to any group.
A senior Turkish government official told the Associated Press that the killing was "fully professional, not a one-man action" and that the attack was well-planned.
However, Russia and Turkey agreed quickly the assassination was an act of "provocation" with Russian President Vladimir Putin saying it was "undoubtedly... aimed at disrupting the normalisation" of bilateral ties and the "peace process in Syria".
They have vowed to work together to find out who is behind the murder of Mr Karlov.
Mr Turkes also paid his respects to Karlov at Tuesday's ceremony, describing him as the man who "has become the eternal symbol of Turkish-Russian friendship".
In his time in Ankara, the veteran diplomat, 62, who had served as Soviet ambassador to North Korea for much of the 1980s, had to grapple with a major crisis when a Turkish plane shot down a Russian jet close to the Syrian border.
Demanding a Turkish apology, Moscow imposed damaging sanctions - notably a freeze on charter flights by Russian tourists - and the two countries only recently mended ties.
Turkey's foreign minister has told the US Secretary of State John Kerry that Ankara and Moscow believe followers of Muslim cleric Fethullah Gulen are behind Mr Karlov's killing.
Ankara has also accused Fethullah Gulen of orchestrating a failed coup in July - a charge the cleric denies.