A Green Point family opened their front door to what appeared to be a uniformed policeman, but a trio of armed robbers barged in instead.
They took two cars and valuables including cellphones and a laptop computer in the surprise raid on Wednesday.
After an all-points bulletin alerting nightshift patrols to the attack and the stolen cars, police found both vehicles abandoned in Observatory and Woodstock side streets an hour later, but there was no sign of the gang.
Then early on Friday, a dog unit police patrol in Goodwood spotted suspicious-looking men in a Ford Lazer in Vanguard Drive shortly before 1am and pulled them over near the Wingfield military base.
The driver of the car was in a police uniform. The policemen checked the car and discovered it had been stolen in Parow last month.
The driver and two other occupants were arrested.
Detectives are trying to link the trio to the Green Point attack.
In what may mean a breakthrough, a batch of allegedly stolen identity books were found in the car, many with the photographs removed.
Detectives believe the ID books could help crack a series of unsolved crimes, including home robberies, some of which involved a suspect posing as a policeman.
The bogus policeman and his two accomplices were taken into custody at the Goodwood police and were expected to be handed to Serious Violent Crime Unit police for further investigation.
The three are expected to appear in court on Friday.