Detective Hilton Botha, who has faced fierce questioning at Mr Pistorius's bail hearing, was allegedly involved in a shooting two years ago.
Mr Pistorius, a Paralympic champion, denies the premeditated murder of his girlfriend Reeva Steenkamp, 29.
His bail hearing in Pretoria is scheduled to resume at 09:00 GMT.Reinstated charges
Police spokesman Neville Malila said that Det Botha and two other officers were due to appear in court in May.
Mr Malila said it was alleged that while driving a state-owned vehicle the three had opened fire on a minibus taxi loaded with passengers.
The three were arrested in 2011, Eyewitness News says, citing police.
Mr Malila told Reuters news agency the charges against Det Botha had originally been dropped but were reinstated on Wednesday by the state prosecutor after the officer had taken the stand.
It is not clear whether Det Botha will continue working on the case.
Medupe Simasiku, a spokesman for the Pistorius prosecutors, told Associated Press they were unaware of the charges and would now investigate whether the detective should remain.
The BBC's Peter Biles in Pretoria says the police statement concerning Det Botha is an extraordinary turn of events.
Mr Pistorius says he shot Ms Steenkamp in the bathroom of his home after mistaking her for an intruder.
If denied bail, Mr Pistorius could face months in prison before a full trial begins.'Extremely concerning'
Correspondents say Det Botha's evidence on Wednesday appeared first to boost the prosecution's case and then offer the defence a hope of winning the argument.
Det Botha told the court that the trajectory of gunshots through the bathroom door indicated that Mr Pistorius, a double amputee, was wearing his prosthetic legs and shot downwards through the door.
This contradicted an earlier account given by Mr Pistorius, who said he was walking on his stumps and grabbed his gun because he felt vulnerable when he thought an intruder had entered.
South Africa's justice system
Jury trials were scrapped more than 40 years ago because all-white juries were seen as unlikely to give black defendants a fair trial
A single judge is considered less susceptible to public opinion or media comments
So the South African media is more free to report details about the Oscar Pistorius case than the media in many other countries where such reporting would be seen as prejudicial
The detective then said a witness had said he heard fighting at Mr Pistorius's home on the night Ms Steenkamp was shot.
Det Botha initially said the witness was some 600m (1,800ft) away, but later amended his answer to 300m after a break for lunch.
Mr Pistorius's family said the changes were "extremely concerning".
The detective was also accused of not wearing protective clothing at the crime scene.
The magistrate appeared to question Det Botha's assertion that Mr Pistorius could be a flight risk who should be denied bail.
The Pistorius family issued a statement saying they were "satisfied with the outcome" of Wednesday's proceedings.
The magistrate has deemed this a "schedule six" case, meaning Mr Pistorius is accused of premeditated murder.
His defence team will have to prove the extenuating circumstances that would justify granting bail.
Oscar Pistorius won gold medals at the 2004 Paralympic Games in Athens, in Beijing in 2008 and London in 2012.
In London he made history by becoming the first double-amputee to run in the Olympics, making the semi-final of the 400m.
