Robbers who shot and killed a Mustang Resources security guard in a Mozambique ruby heist last month are still at large despite a reward offered by the miner.

“The country has never experienced an incident like this, it has come as a shock to all of us,” Mustang’s managing director Christiaan Jordaan told Stockhead.

The killers broke in to Mustang Resources’ (ASX:MUS) ruby mine on September 25, shooting a male security guard to death and escaping with 19,000 carats of rubies.

Mustang, the world’s only listed ruby miner, operates in the Montepuez ruby field in the east African nation of Mozambique — a relatively new source of the red stones.

Mustang had issued a reward of 200,000 Mozambique meticais — about $4000 — for information that could lead to an arrest, Mr Jordaan said.

“We have engaged with the local government and are enhancing security in the local area.

“Even the minister of minerals has expressed the seriousness of catching these people and making sure it never happens again — it does not look good for the country’s trade or foreign investment.”

The security guard had been the breadwinner for his family and Mustang was providing ongoing financial and emotional support.

“Given where we operate, there is increased risk but it came as a shock to everyone concerned,” Mr Jordaan said.

“Mozambique is not a place prone to violence, but you do have in Africa — with a lot of impoverished communities — bad apples that can do bad things.”

The thieves got away with a small safe of low-quality rubies, but Mustang says its upcoming ruby auction in Mauritius from October 27 will be largely unaffected.

“19,000 carats might sound like a lot of rubies but within the area the thieves could easily sell them without questions being asked,” Mr Jordaan said.

Mozambique has been cracking down on illegal mining — 4000 miners are said to have been expelled from the Montepuez region since February.

“There is still the presence of local buyers that the police are trying to cut down on.

“[But] the situation has substantially improved and illegal mining has started to dry up.”