48-year-old Singh, who was ACP in Delhi Police's Special Operations Squad and had been provided 'Z' category security cover, was shot twice in the head from point blank range last night allegedly by property dealer Vijay Bhardwaj.

The incident took place in Bhardwaj's office near Sukhrali village in Gurgaon in Haryana at around 10:30 pm last night, Delhi Police spokesman Rajan Bhagat said. It was not immediately clear whether the men guarding him were present when he was shot.

Gurgaon Police Commissioner Mohinder Lal told PTI that Bhardwaj has surrendered and "confessed" to the crime.

"The accused has surrendered and confessed to the crime.

It appears that the dispute was over the profit both of them got in a property deal," Lal said.

"He also said that he was trying to arrange the money to give to Singh for a long time and he could not," he said.

Talking to reporters, Bhardwaj claimed he owed some money to Singh and that the officer had "threatened" to kill him.

"I wanted to commit suicide, but my family found the (suicide) letter and stopped me. Today was payment day and I could not put the money together. He said he would kill me," he claimed.

Lal said Bhardwaj had allegedly procured the revolver three days back from Singh and used the weapon to kill him.

Singh, who had joined Delhi Police as a Sub-Inspector in 1982, had 56 encounter killings to his name, including the infamous Ansal Plaza operation in 2002 in which two terrorists were killed. However, questions were raised over some of his operations by human rights groups.

A winner of five medals, including the President's Police Medal for Gallantry, Singh was involved in the investigations into the Parliament and Red Fort attack cases.

The Assistant Commissioner of Police was transferred from the Crime Branch to Delhi Armed Police after allegations of his involvement in an illegal land deal last year. There were also allegations of his links with drug traffickers, land mafia and bookies following telephone tappings.

The vigilance probe, however, gave him a clean chit and he returned to head the Special Operations Squad in November last year.

Delhi Police said it would work closely with Gurgaon Police in the investigation into the killing.

A Delhi Police team which went to verify details about the incident identified his body which has been sent to the civic hospital in Gurgoan for post-mortem.