The correct option is A given the green light, red-handed
The sentence implies that the police were permitted to interrogate Renu. Therefore, we can use the idiom 'given the green light' to convey the same. Also, the sentence implies that Renu was caught while stealing a diamond. The idiom to mean that someone was caught while doing something wrong is 'red-handed'. Hence, 'given the green light, red-handed' is the correct answer.