Police filing case against me after I met with an accident

On 17th April, I was driving a two-wheeler while my female cousin was with me as a pillion rider. I suddenly approach the breaks and we fall. Due to not wearing any helmet, my cousin got a minor brain injury and got admitted to the hospital ICU. Meanwhile, one traffic police came and seized my vehicle and asked me to collect it from Poonamalle traffic investigation office with the discharge summary of my cousin. But after she got discharged, I went to them all vehicle papers and discharge summary of my sister, but they are asking me for my driving license to release the vehicle. My sister and me also given a letter that we do not want any investigation. Are they authorized to ask for the driving license now as they didn't ask for it before? Ethically I know, you may think I am the culprit riding without a license but through the law can they really seize my vehicle and throw cases on me, because I don't have a DL. They threatened me with arrest even.