COLOMBO, May 8 (Reuters) – Sri Lankan shares extended falls into a fifth session on Wednesday and closed at their lowest levels in six-and-a-half years on shattered investor confidence following the Easter Sunday bombings. ** Investigators have dismantled a major part of the network linked to the Easter Sunday bombings, Prime Minister Ranil Wickremesinghe said on Tuesday, but warned the chance of further Islamist militant attacks could not be ruled out. ** The benchmark stock index ended 0.18 percent weaker on Wednesday at 5,372.97, its lowest close since Dec. 5, 2012. ** Turnover was 222.3 million rupees ($1.27 million), lower than this year’s daily average of 571.2 million rupees. Last year’s daily average was 834 million rupees. ** Foreign investors bought a net 60.2 million