Apparently depressed over some family problem, a colonel on Friday allegedly committed suicide by shooting himself in the city.RK Vajpayee (40), who was posted in Guwahati, shot himself with his license rifle when he was alone at his residence, police said.Later, family members rushed Vajpayee to the hospital where doctors declared him brought dead.Preliminary investigations indicated that Vajpayee was upset due to some family problems, cantt police station circle officer Dharmendra Singh said.