Mumbai, The Central Bureau of Investigation (CBI) on Wednesday slammed the Mumbai Police for registering an FIR against late Bollywood actor Sushant Singh Rajput's sisters on the complaint of Rhea Chakraborty, saying it is "vitiated" and "bad in law".

The CBI made the submissions in the Bombay High Court while opposing the second FIR filed by Mumbai Police on the complaints of Rhea related to the death of Sushant.

The CBI informed the court that the present FIR has been registered by Mumbai Police in complete disregard to the provisions of Section 154 of the CrPC.

It said both respondent Rhea and Mumbai Police were consciously aware that an FIR has been registered by the Patna Police to look into the circumstances surrounding the death of Sushant, which has been transferred to the CBI for investigation.

The agency said that the probe by the CBI was approved by the Supreme Court on August 19.

"Therefore, registration of another FIR on the same facts and cause of action was neither warranted, not allowed under the law. Thus the FIR is vitiated and bad in law," the CBI said.

The probe agency also said that the allegations against the late actor's sisters in the FIR registered on the basis of Rhea's complaint are "presumptive and speculative".

"Pertinently, the allegations levelled in the instant FIR are most presumptive and speculative in nature," it said.

The CBI also argued that the Mumbai Police have not registered an FIR as an outcome of the inquest proceedings being conducted by them. Therefore, the Supreme Court judgement of August 19 does not allow registration of any such FIR.

The CBI's reply came in the court after Rhea on Tuesday urged the Bombay High Court not to dismiss her case against Sushant's two sisters -- Meetu Singh and Priyanka Singh -- whom she has accused of helping the actor illegally access anxiety drugs using fake prescriptions from one Tarun Kumar in Delhi.

The CBI in its reply also stated that if Mumbai Police or Rhea had any information on the death of Sushant, they should have been directly shared with the CBI for action. The FIR registered at the Bandra police station was not required, it said.

The CBI also said that it received an application from Rhea dated September 14 through Mumbai jail authorities to "drop or delete" Section 306 of the Indian Penal Code in the FIR filed by the Mumbai Police on her complaint.

The CBI stated that the procedure of dropping a penal section of law during investigation is a process unknown to law and the same cannot be done by the investigating agencies.

"An FIR which has been registered can either be quashed by Constitutional courts or culminate into a report under Section 173 of the CrPC. Therefore the request of Rhea to drop Section 306 from the FIR cannot be acceded to," it said.

The CBI also said that it is conducting an investigation wherein Section 306 has been invoked in the FIR. "Thus the role of each and every person, whosoever had instigated or abetted the commission of suicide by Sushant, is being investigated," it said.

The CBI also stressed that the agency is conducting investigation meticulously and professionally without being hindered by any external factor and would thoroughly go into each and every aspect relating to the death of Sushant in a fair and impartial manner.

The Mumbai Police registered a case against Sushant's sisters on the complaint of Rhea alleging that they were helping the actor access anxiety drugs illegally using fake prescriptions.

Rhea's complaint was based on WhatsApp chats between the actor and his sister on June 8 -- just six days before he was found dead at his Mont Blanc Apartment on June 14.

The alleged chats between Sushant and his sister indicated that she had advised her brother to take three medicines banned under the Narcotic Drugs and Psychotropic Substances Act.

In her complaint, she pointed out that the alleged chats of Sushant and his sister were opposite to the family's claim that they were unaware of the late actor's mental health issues.

The CBI had registered a case on August 6 after notification from the Centre on the request of Bihar government.

The Bihar Police registered a case on the basis of the complaint filed by Sushant's father K.K. Singh on July 25 against Rhea, her brother Showik, father Indrajit, mother Sandhya, Sushant's house manager Samuel Miranda and former manaqger Shruti Modi, among others.

A CBI team went to Mumbai on August 20, a day after the Supreme Court gave the nod for the federal agency to probe the matter.

The CBI team has recorded the statements of Rhea, Showik and several others in the case.

Besides CBI, Rhea is also being investigated by the Enforcement Directorate (ED) and the Narcotics Control Bureau (NCB). Rhea and her brother were arrested by the NCB. While Rhea was granted bail after 28 days, Showik is still in judicial custody.