A rogue elephant has killed at least 16 villagers in the past two months in Jharkhand after likely being expelled from his herd "for bad behaviour", a wildlife official said on Thursday.The mature male, believed to be 15 or 16 years old, has been on the rampage in the state's tribal Santhal Pargana region ever since he was separated from the herd of 22 elephants."It's likely he was in heat and was expelled because of his bad behaviour or sexual rivalry with other males," Satish Chandra Rai, regional divisional forest officer, told AFP."We are studying his behaviour and a team of 20 officials is constantly trying to track him because our first priority is to protect the animal."The elephant, which is now on its way back seeking to reunite with the herd, has managed to outwit officials with his sheer speed and unpredictability.On Tuesday, the tusker lifted an elderly couple with his trunk and killed them when they had ventured out before dawn.Mr Rai said the elephant was only killing people who accidently got in its way, got too close, or who tried to provoke it and take pictures."He has not been breaking into houses or deliberately attacking people," Mr Rai said."We want to see if he is accepted back in the herd. If he is not it will be proved he is a bad boy."India has an estimated 30,000 wild Asian elephants -- nearly 60 per cent of the total wild population.In recent years there have been rising incidents of elephants killed by locals -- and vice-versa -- as humans encroach further into forest areas.