The man told the police that he had a quarrel with the victim.
The police on Saturday arrested a security guard who had allegedly killed a fellow guard in city's Sheetala Hospital in the city on Friday.
Naufil Anwar was arrested from Sikandarabad in Bulandshahr district of Uttar Pradesh on Saturday.
Anwar told the police that he had a quarrel with victim Jugal Kishrore.
"Anwar has told us about the fracas he had with Kishore. After leaving for the day from duty, the accused returned to the hospital around 5 a.m. without informing his family. He was carrying a sharp knife in a bag," said Subhash Bokan, PRO of Gurugram police.
"Anwar initially stayed for a few minutes at the hospital gate. As per CCTV footage, he went out of the hospital at 5.15 am and returned four minutes later. The accused straight away went to the third floor and stabbed Kishore over a dozen times until he died," Mr Bokan said.
The police said Mr Kishore had tried to run out of hospital to save himself, but Anwar had overpowered him. "During the scuffle, chairs, flower pots and medical equipment were found scattered around. Stair-steps were splattered with blood, police said.
Sources said at the centre of enmity between the two was a girl who was in touch with Mr Kishore. Anwar disliked the relationship.
"We have arrested the accused and are trying to find the weapon used in the crime. The accused will be produced in the Gurugram civil court on Sunday," Mr Bokan said.