A retired engineer and a policeman deployed for his personal security were shot dead at the former's home in a Noida village, police said on Wednesday.Four persons have been arrested and were being interrogated, a police official told IANS.The assailants pumped six bullets into retired engineer Raj Kumar Sharma late Tuesday night in Surajpur Junpat village, where he lived with his family. His security guard Nitin Verma was shot thrice.Police said Sharma's son Narendra was killed in December 2013, and the case was pending in a trial court. The retired engineer was provided five police personnel for protection. The unidentified armed assailants arrived in a Swift car late Tuesday night and barged into Sharma's house. They shot him six times while his guard was shot thrice when he reacted to the shootout. The assailants then fired indiscriminately and fled the spot, police said adding that at least 40 rounds were fired.Both were declared brought dead at a nearby hospital. The bodies were sent for post-mortem. Police said they suspected the hand of Anil Dujana gang in the murders.