AFP Copyright: AFP Lambert Mende has filed a complaint for the way he was treated by the police Image caption: Lambert Mende has filed a complaint for the way he was treated by the police

Last Sunday former DR Congo Communication Minister Lambert Mende was about to have lunch when he was kidnapped from his home - so he claims.

He later told reporters he was tortured by police officers and the man responsible was interim Interior Minister Basile Olongo.

Mr Olongo acknowledged sending officers to detain Mr Mende following an investigation over a suspected diamond in his possession.

He did, however, criticise Mr Mende's treatment and a senior police officer has since been suspended.

Mr Olongo says the diamond was discovered by artisanal miners in the province of Sankuru - where Mr Mende is running to be governor.

The miners, the minister says, had travelled to the capital, Kinshasa, for a meeting with government officials since they didn’t have the correct authorisation to sell the gem.

According to Mr Olongo, they were instead lured to Mr Mende’s house.

The former minister's aide said the miners "are from his constituency".

The stone in question is about 90 carats - about the size of a ping-pong ball, according to the country’s precious minerals evaluation and certification centre (CEEC) which analysed it on Wednesday.

To the surprise of many, however, they also concluded it was not a diamond.

Georges Kapiamba, lawyer and president of the Congolese Association for Access to Justice (ACAJ), says the story doesn’t stop there.

He believes the real diamond, potentially worth millions of dollars, has disappeared and that the certificate claiming it isn’t a diamond is bogus.

“This analysis is a scam, we completely reject it… Members of the CEEC were appointed by the previous government, of which Mende was part. The diamond is being hidden to be sold on the black market,” Mr Kapiamba told the BBC.

He did not provide any evidence to back up his claim but called for an investigation.

Mr Mende’s personal secretary, Frank Diefu denied that claim and said the stone - quartz, according to them - was in the hands of the provincial minister of mines, or with the CEEC.

Mr Kapiamba says he will file a complaint with the prosecutor’s office by the end of the month.

Mr Mende – who has parliamentary immunity - has also filed a complaint for the way he was treated by the police.