Additional deputy commissioner of police (north east Delhi) RP Meena said the incident was reported around 2 pm on Saturday.
The deceased, Atif, was shot in the head allegedly by his brother-in-law Akram at Meet Nagar in Delhi. The victim was rushed to GTB hospital where he died while being treated for his injuries, the officer said.
20-year-old Akram was arrested on Tuesday from Ghaziabad's Dabur Talab at Loni. A country-made pistol, which was allegedly used in the crime, was recovered from him, Mr Meena said.
During interrogation, the accused said his younger sister had married Atif against the will of his family which prompted Akram and his father Rahisuddin to conspire and kill Atif, the police said.
"He invited his sister and Atif to settle the issue and carried a loaded pistol. When Atif and his wife reached at the designated spot for the meeting, after some brief talks, Akram shot Atif and fled from there," RP Meena said.
(With inputs from PTI)