The head constable was posted and serving the family of the judge for two years.
Both of the injured have been taken to the hospital, the son is in a. critical state.
The incident took place around 3:30 pm near Sector 49, Gurgaon, where the wife and son of additional sessions judge Krishan kant Sharma had gone shopping.
The gunman first shot the wife and then the son, in front of several eye-witnesses. Immediately after that, he tried to drag the judge's son in the car.
But when he couldn't, he left the judge's son on the road and drove away in the same car that they had come to the market in, show video footage captured by eyewitnesses from their cellphones.
The head constable called the judge to say, "I have shot your wife and son". He made two more calls telling people about the shooting.
After shooting at them, he reached a police station where he fired again. The Station House Officer tried to capture him but eyewitnesses say that the police force was too scared to catch him as he had a weapon in his hand.
He was later arrested from Faridabad road a little while later.
Misuse of security
The police said they are still investigating the killings. But many in the security apparatus are saying that politicians and judiciary misuse their police staff as servants. They are treated as waiters, drivers and peons and many resent this. Though the policemen maintained anonymity they said that this could be a possible reason for the murders.
Initial investigations suggest that he was suffering from depression and was upset at the "misbehaviour" by the judge's family.