Facts forming parts of the same transaction = The doctrine of Res Gestae.
The literal meaning of Res Gestae is - things done
Res gestae is a doctrine developed under English law and can be understood more clearly from examples and case laws.
Ex-A was running with a knife towards B and B was shouting save me and C heard it from a distance, So, since c heard it, he can be called a witness for the crime. Thus, whatever C heard will come under Res gestae.

Other relevant illustrations are:

• Victim's or injured person's cry for help.
• Sound of a shot of a bullet.
• Witness's cry while seeing a crime happen.
• Gestures, etc., of a person in need of help.

Therefore, Whatever is happening and whatever is said or heard everything will come under RES GESTAE.

The doctrine of Res Gestae took time to evolve further. Earlier, it was stated that Res gestae only means whatever is done/heard or said during the crime.

After the crime is committed or completed then whatever is said or heard will not be counted under res gestae. Let us understand this through case law. Case law:

• R vs Beddingfield (1695) 6 Skin 402
  • A couple were living together happily. After a certain time, things got worse, and one day during a heated argument, the man tried to cut the woman's neck.
  • Escaping, the woman tried to run away to save herself. While running, she saw her aunt and told her what her boyfriend had done.
  • The woman's statement to her aunt was not accepted as res gestae since it was given after the completion of the crime.
  • The court concluded that things said or heard after the completion of the offence will not amount to res gestae.
     
• Ratten vs Queen (1971) 3 WLR 930
  • This case changed the perspective of Res Gestae.
  • A telephone operator of the police department received a call from a panicked woman who demanded to talk to the police.
  • As soon as she provided her address, the call was disconnected. Under suspicion, police officers were sent to her address and found her dead—shot by a gun.
  • The husband claimed he was cleaning his guns and accidentally fired the bullet that hit her.
  • The court examined whether the woman had apprehension that she might be killed or if it was a coincidence.
  • The court concluded that the woman's words formed part of res gestae and included things that took place immediately after the offence.
     
• Other similar cases:
  • R vs Christie
    • A child reported sexual harassment and inappropriate touching to her mother.
    • The court ruled that such a statement would not amount to res gestae since it was given after the completion of the offence.
       
  • R vs Foster (1834) 6 C & C 325; 172 ER 1261
    • A truck driver was driving at high speed and rammed into a car.
    • The victim's wife, who was standing at the corner of the road, did not witness the accident but saw the speeding truck.
    • After the accident, she ran to her husband, who told her that the particular truck had rammed into his car.

So, the question is will the husband's statement come under Res Gestae since it was given after the completion of the offence? and since his wife was not an eye-witness of the accident?

Court ruled that, Yes this statement will form a part under res gestae because this was said immediately after the offence.

So, this brought us to the evolved part of the doctrine and concluded that whatever is said or heard or happened immediately after the offence will also form a part of res gestae.
Immediately means when the person doesn't even have the time to think, it should be a sudden reaction. And hence Res gestae will also be called an exception to the hearsay rule of evidence.

Conclusion:
Section 4 of Bharatiya Sakhshya Adhiniyam deals with the doctrine of res gestae under the title – "Facts forming part of the same transaction" Res Gestae is also an exception to the hearsay rule of evidence.

Res gestae is important because it helps us understand how the judicial system tries to accumulate and examine relevant information available during the happening of an offence. It helps us understand the evidence available during the commitment of an offence on a deeper level.