A domestic help was allegedly raped by her employer for about two years at his flat in a two-storey building in the city's Halishahar area.
As the victim told her uncle, a security guard of the building, about her ordeal on the night of December 29 last year, he also allegedly raped her.
This only came to light on Thursday night when the girl's father filed a rape case with Halishahar Police Station against the two alleged rapists.
Police on the same night arrested the security guard from his rented house in Halishahar. However, the other accused went into hiding.
Law enforcers said the father used to visit her 17-year-old daughter once or twice a month, but she didn't tell him about the sexual assault for fear of losing the job.
To support her day labourer father financially, the girl went to the house in Halishahar's Madhyam Rampura area on January 01, 2017 to work as a domestic help.
Her father had no worries over sending her to the house as his younger brother, 40, was a security guard there.
The girl was raped by the 63-year-old homeowner many times till last month when his family members were away from home, police said.
Ashikur Rahaman, assistant commissioner (Double Mooring Zone) of Chattogram Metropolitan Police, said the victim was sent to One Stop Crisis Centre at Chittagong Medical College Hospital for medical examinations.
According to the case statement, the homeowner from Chattogram's Mirsarai upazila had been sexually assaulting the girl since she joined work.
He had threatened the victim of sacking her if she disclosed the incident to others.
The victim's uncle took her to his rented house in the city's Halishahar area on December 30 last year. The girl disclosed the whole incident to her father on January 16 when he went there, read the case statement.
CMP AC Ashikur said they were investigating the incident as a high priority and were trying to arrest the other accused.
According to a report of rights body, Ain o Salish Kendra, 732 women and children were raped from January 1 to December 31 last year. Of them, 203 women and children were gang-raped.
The report, released on January 10, also said 63 were killed after rape, while three were killed after attempted rape.