Seoul, Jan 13, Samsung heir Lee Jae-yong, returned home on Friday after facing marathon questioning by prosecutors all night about his possible involvement in a corruption scandal that led to the impeachment of former South Korean President Park Geun-hye.

Lee was called to testify on Thursday over suspicions that the country's largest family-run conglomerate gave financial support to Choi Soon-sil, Efe news reported.

Choi nicknamed the "female Rasputin" is being considered the apparent brain behind the plot involving business favours using her close relationship with Park.

The prosecution believes that the Samsung group signed a contract worth $18.6 million with a company based in Germany owned by Choi and also provided financial support for the equestrian training of her 20-year-old daughter.

Samsung also donated $17.3 million to two non-profit foundations operated by Choi.

However, the Samsung chief insisted that they thought the money was given for good causes such as promoting local culture abroad and the sports sector.

It was suspected that the contract was being signed in exchange for support from the National Pension Service for a major merger agreement between Samsung's subsidiaries in 2015.

Samsung admitted the donations but denied that they had been made to secure return favours in the merger process.

The prosecutor, however, has not yet decided whether or not to detain Lee, something that could be a blow to Samsung.

Lee Jae-yong took over the reins of the Samsung conglomerate after his father Lee Kun-hee in May 2014 suffered a heart attack, which still keeps him hospitalised and speechless.

The "female Rasputin" case sparked outrage in South Korea and led to Park's impeachment in December 2016. Park is now waiting for the South Korean constitutional court to decide whether the impeachment vote is valid.