Introduction

The DNA specimen plays a very important role in cases such as sexual assault, homicide, mass disaster, missing person identification, etc. Though, the achievement for a forensic laboratory examiner is depended on the condition of the evidence, if the DNA evidence is in a good condition then the maximum chances of a successful DNA profiling takes place. But if the collection and preservation of the evidence are not in an appropriate way then the DNA evidence might be able to give better results. All the biological evidence is at a risk of deterioration which results in microbial growth and this occurs due to environmental conditions. So, careful storage, collection, and preservation are important to obtain useful information for DNA analysis. A standard operating procedure is required for DNA collection and preservation in several types of the scene of crime and these procedures should be followed by medical doctors and investigation officers in the course of a criminal investigation. The DNA material is generally extracted from the biological samples. The biological samples from which DNA material is extracted and analyzed are such as blood and bloodstains, tissues and cells, hair with follicles, semen and seminal stains, bones and organs, saliva, etc. In case of bite marks the saliva is present on the person’s clothing or skin. Blood, saliva, hair, sweat, vaginal fluid, and semen can be found on the pillow, bed cover, blanket, etc. in rape cases. In the crime scene investigation, DNA evidence plays a very important role, it helps in connecting the victim and perpetrator with the crime scene and helps in legal proceedings. And it also helps in the reconstruction of the crime scene and supports the statement given by perpetrators or suspects, victims, and eyewitnesses. The collection of evidence should take place step by step by the field investigator at the scene of the crime (Lee & Pagliaro, 2013).

The priorities of an investigator are to discovering the evidence, recognizing the evidence, examining the evidence, collecting the evidence, recording the evidence, identifying the evidence, and packaging and storing of the evidence, present the evidence in the court of law. To avoid the contamination proper handling of the evidence should take place at the crime scene investigation. The main purpose of the DNA evidence is to provide useful information that helps in connecting the perpetrator or suspect and victim with the scene of crime. Every scene of crime is unique. There is a need for proper marking, sealing, and packaging of evidence at the time of collection of evidence. After that send the evidence to the forensic science laboratory. The work of a forensic scientist starts from the scene of crime with evidence recognition and recovery. Sometimes the evidence left by the suspect at the scene of crime. After the collection of the evidence, they have to be properly analyzed in the laboratories. DNA evidence also helps in revealing the information related to corpus delicti, modus operandi, connecting or linking the perpetrator with the victim and weapon, helps in disproving or supporting the testimony given by the witness, helps in a personal identification of the suspect, proving a lead in the investigation. Blood is an important piece of evidence that is found on the scene of crime and it can be found on surfaces such as vehicle, weapon, soil, cloth, dead body, windows, wall, etc. If blood is found in the form of liquid at the scene of crime, then with the help of dropper collect the blood and stored in plastic or glass bottle after adding the suitable anticoagulant i.e. EDTA. And stored the blood evidence in dark and cool places because it gets destroyed in heat or when directly exposed to light. The semen preservation is always taking place after drying the semen stain completely. In case if semen stain is wet the chances of bacterial growth are possible and due to the protein present in semen, the stage of putrefaction may also occur. The semen preservation is always taking place in airbag, not in a plastic bag or airtight bag. If stain was found on a small article, preserved the entire article and send the sample in a forensic science laboratory. If semen stain is present on an immovable object, then with the help of a scalpel or sharp knife scratch the semen stain and packaged in a clean bottle of glass. A clean plastic tube or bag is also used in the preservation when a semen stain is present on the public hair. When the semen stain is present on any part of the body than with the help of cotton swab and saline water the stain can be collected. Do not touch the sample with bare hands because it results in contamination of the sample or sometimes it can have destroyed the evidence (https://www.epgp.inflibnet.ac.in).

In biological samples, DNA played a vital role in acute sexual assault (ASA) cases which help in establishing the incidence of sexual interaction and also helps in the identification of the suspect. There are the techniques which are used to collect the DNA evidence,

One Swab – It is a quick technique but this technique does not give a guarantee in collecting the whole evidence for analysis in the laboratory. It is mainly used when the evidence is present in limited quantity

Two Swab – This technique is applied when there is abundant biological sample is present such as in cases where direct ejaculation was found in the vaginal cavity and this technique is only applicable to post pubertal victims. In this technique, the specimen is quickly collected and permits the usage of the second swab for counterproof.

Two Swabs Successively – This is also known as the double swab technique, it is the application of two successive swabs, and the first one is the wet whose target is to gather the evidence in the majority and the second one is a dry swab. This method has aimed to collect evidence in an abundant amount. It is not a rapid technique and there is no such guarantee of two swabs equality, the second swab can have evidence in a lower concentration. After having limitations, this technique is widely used for the purpose of the collection of numerous types of biological specimens (Magalhães et al., 2015).

To get the maximum information about the DNA profile from the biological samples collected from the scene of the crime, use a device that gives more significant results. This is vital to preserving from degradation and pollutants to maintain the integrity of the biological sample which helps in DNA analysis. So to make a successful DNA profile, the sample is not relaid completely on the laboratory examination processes but also depends on the sampling methods applied by the investigator at the scene of crime. Several types of collection methods are available such as FTA paper scraping, cutting method, scraping the surface with the help of a wooden applicator stick, taping, dry or wet, double or single swabbing, vacuum sampling. Swabbing is the maximum used versatile method. It is helpful in the collection of DNA samples which is used by both the forensic laboratory examiner and crime scene investigator. So, as a result, there is an increase in the swab type’s methods, they are available in the markets. There are several studies conducted on the swabs and the swabbing conditions and questions are always arising on the institutions that the swabs methods are still suitable, whether they are giving good scientific results or not. There are some swabs that are used in the collection of DNA traces from different items. The swabs such as Puritan FAB-MINI-AP, COPAN 4N6FLOQ Swabs (Genetic variety), and Sarstedt Forensic Swab are used for the purpose of DNA traces collection (Comte et al., 2019).