Although the Gurgaon police had disclosed that Delhi Police officers had let off the kingpin after taking bribe, Delhi Police officers had denied it.

Today, Delhi Police tried to put up a brave front. "We have been following the policy of zero tolerance for corruption and wrong-doing," Garg said.

According to ASI Singh's confession, one of the constables of the team, Devender, told him about the possible kidney racket running from the DLF house of Dr Amit Kumar. Devender was earlier posted at Nizamuddin Railway Station where a case against Dr Amit's key accomplice Dr Upender Kumar was registered in 2000.

Could you tell me what "front" means here?
I think of a facade - or the fake building fronts they used to use when shooting an old cowboy movie in a town that didn't really exist. One constructs something fake, trying to make it look real enough to convince someone that it is real. It may be something physical, or it may be an act which a group of people put on to fool someone. Have you seen the old movie, The Sting?

We also use it to describe a business which is simply a cover for some illegal operation, such as a massage parlor fronting for a house of prostitution.

In the police case described, it sounds like they're just stonewalling, or denying any wrongdoing, claiming their policy is not to allow corruption.
"To put a brave front on something" is the same as"to put a brave face on something" - you are trying to be positive in your behaviour or speech, even if you think/know there is a problem.