Supplementary expert report in Narin Güran murder case added to court file

The uncle Salim Güran, mother Yüksel Güran, brother Enes Güran, and neighbor Nevzat Bahtiyar, who are in custody in connection with the murder of Narin Güran—who went missing on August 21 in the Tavşantepe neighborhood of the central Bağlar district and whose body was found in the Eğertutmaz Stream on September 8—are being tried on charges of "intentional killing of a child in complicity," facing life imprisonment with aggravated conditions.

In an interim decision, the Diyarbakır 8th High Criminal Court requested that a warrant be issued to the Diyarbakır Chief Public Prosecutor's Office, demanding a detailed supplementary report from those who prepared the narrowed-down cell site location report. The court requested information on the methods and base station data used, the devices and criteria applied, the scientific techniques employed, and an assessment of the possibility of any margin of error.

In accordance with the interim decision, the supplementary expert report prepared by sworn experts has been completed and submitted to the Diyarbakır 8th High Criminal Court. The report notes that mobile phones connect to the mobile network via base stations, transmitting data between phones and base stations via radio frequencies. It explains that when a user makes a call, sends a message, or connects to the internet, this information reaches the base station via radio signals and is then transmitted to the operator's main communication network.

Stating that one of the methods for determining geographical location using base stations is the "Triangulation" method, the report provided the following information:

"When a mobile phone is connected to at least three different base stations, the operator can determine the phone's approximate location using distance information to these stations. A distance is calculated based on the strength and propagation time of the signal from each base station, and this information is then used to determine the region where the phone is located. Factors considered include that calls made via GSM lines receive signals from the nearest base station if the primary one is congested, that moving between locations causes the device to leave one coverage area and enter another, and that while signal loss is often due to external factors, it can sometimes be caused by hardware or software issues within the device, such as faulty antennas or software glitches affecting signal reception."

During the narrow-area base station detection study, all base stations in the Tavşantepe neighborhood and globally were identified one by one in light of data obtained through various licensed programs designed for HTS analysis, such as 'Open Signal', 'Network Cell Info Lite', and 'Netmonsters'. Signal strength values and signal cell information, as shown in the visuals, were evaluated individually. The obtained cell information was analyzed one by one using a systematic matching and separation algorithm in a Microsoft Excel worksheet, and the potential locations of the phones used by the individuals involved in the incident were evaluated."

The report, which states that visits were made to the Tavşantepe neighborhood on August 29-30 and on September 8 and 9—the date Narin Güran's body was found—noted the following:

"A narrowed-down base station study was conducted for all suspects, covering the residences of Salim Güran, Arif Güran, and Nevzat Bahtiyar, as well as intermediate areas and streets, at different days and times, both day and night. Especially while working in and around the homes of Arif and Salim Güran, factors such as having officials in the area turn off their mobile phones to prevent congestion at the base station were taken into account. Using different programs and at least two lines, step-by-step work was carried out in and around the homes and outbuildings of Arif and Salim Güran and Nevzat Bahtiyar, as well as on the connecting roads. After hundreds of operations, the main base, side base, and GPRS base stations were identified meticulously and clearly without room for error."

The report states that the village's location on a hill, its ability to receive signals from many base stations in the city center and surrounding areas, and the high number of base stations facilitated the narrow-area base station analysis in the indicated locations; it further notes that if there had been fewer base stations, such detailed work would not have been possible. Additionally, it was stated that because the area where Narin Güran's body was found is located below the village, the base stations could provide coverage over a slightly wider area, and that base station analysis in areas such as the location of the body and fields could not be conducted in great detail due to the vastness of those regions.

The report explains that during the analysis, all base stations, their signal strengths, and signal cell values were identified and analyzed individually.

SIGNALS RECEIVED FROM 22 DIFFERENT BASE STATIONS

The report, which includes the statement, "Tavşantepe Village does not receive signals from just one base station, but from at least 20 different base stations," shared information regarding the 22 base stations from which signals were received. The report also noted that these base stations were registered and listed in the HTS records obtained from the Information and Communication Technologies Authority (BTK) for the suspects.

Base station records for Arif Güran's residence and outbuildings on the day of the incident

The report included the following information regarding signals received from Arif Güran's residence and outbuildings:

"It was determined that Salim Güran arrived at Arif Güran's residence around 15:20 on the day of the incident, moved to the barn area around 15:22, was inside the house between 15:22 and 15:26, entered Arif Güran's residence around 15:36, was at Arif Güran's residence when he spoke with Mehmet Selim Atasoy around 15:52, was at the back of Arif Güran's residence around 16:08, and was in the cornfield near Uzunbahçe around 16:35. Nevzat Bahtiyar was determined to be on the road between the residences of Arif and Salim Güran and near Arif's house around 15:10 on the day of the incident, near Arif's residence around 15:18, at Arif Güran's residence and outbuildings around 15:27, and in the area where Narin Güran's body was found around 16:00."

The report also shared the following information: "Since comparing base station numbers alone would lead to errors, the determinations were made by evaluating data on signal strength obtained from our measurements in the region, the sequence of base station transitions in the individual's HTS report, the distinction between intermediate, main, and side base stations providing service to the region, and other relevant factors."

The report states, "We would like to emphasize that there can be no room for interpretation in narrow-area base station studies; the results of the work are directed by the calls in the HTS records and the density or variability of the base stations. It is important to know that having many base stations provides an advantage and convenience in determining the location of events and individuals. We also note that when conducting these studies, there may be a margin of error of approximately 2 meters and 1 minute due to transitions and mobility between base stations." The report further notes that the information in the initial report, which stated that "the phone used by Salim Güran gave a signal from the cornfield where Narin Güran's body was found between 22:47 and 22:55 on August 21," refers to the field near the location where Narin's body was discovered.

The report stated, "Regarding the Narin Güran murder, no evidence other than the HTS records in the file and Salim Güran's initial statement has been examined; no samples have been taken from statements, nor have any minutes or reports been obtained regarding camera footage. Only the data obtained as a result of our field work has been reported."

News Source: İHA