Congress Vice President Rahul Gandhi on Tuesday said that those responsible for the murder of National Investigation Agency (NIA) officer Tanzil Ahmad must be brought to justice."Brutal murder of NIA officer Tanzil Ahmad investigating key terror cases including Pathankot is extremely shocking," Gandhi tweeted. "My heartfelt condolences to his family. Those responsible for his murder must be brought to justice," he added. Ahmad was returning with his wife after attending a wedding function near Sahaspur town of Bijnor late Saturday night when assailants on motor bikes pumped over 20 bullets into him, killing him. His wife also sustained serious injuries. Police have termed the killing a planned attack.