New Zealanders made 8.16 billion minutes of calls and sent 11.3 billion texts in 20161, that is on average about 1800 minutes of calls and 2500 text per person. Each of these call and text activities has data associated with it and it is a large source of evidence that can be used in courts. Yet, in New Zealand, mobile data is not widely used.
In USA over a million requests for mobile phone records are made every year2. On a, pro rata basis this equates about 15,000 requests in New Zealand. The author does not believe 15,000 cell phone record requests are made in New Zealand, highlighting the under utilisation. Even when mobile data is used it is primarily confined to time of call, who was called and content of the text and very rarely location information is used. The fact that laws governing the retention of mobile call data does not require the retention of location information underlines the lack of understanding.
When a new technology emerges as a forensic tool, it takes time before it is well accepted and wide used in the court system e.g. DNA. However, one would expect New Zealand to be a fast follower, but that is not the case when it comes to making use of mobile call location data. In countries like USA and UK, the legal system has a greater appreciation of mobile call location data and it is regularly used in domestic violence, murder, robbery, drug and rape cases. The level of acceptance of mobile call data as evidence has reached a point where in some court cases mobile call location data was the primary evidence.
Laws around retention of mobile location data
When a call or text or data activity takes place, the mobile phone makes contact with the mobile network. A mobile network has many transmitter towers (cell sites) which serve the mobile. Generally, the mobile is served by the closest cell site. The network operator collects information on time of the activity, duration, cell sites that served the call, called party etc. The length of time this information is retained by the network operator varies.
In New Zealand, there is legal no requirement to retain the cell sites that served the call or text (the location information). The length of time and the amount of data retained varies, and it is determined by the operator’s business practices. Significant amount of location related information is collected by the operators, however, this detailed information is discarded within days. Some operators keep cell sites that served a call and text. However, if multiple cell sites served a call, only the cell sites at the beginning and end of the call are kept.
In contrast, USA, UK and Australia have laws governing the retention of mobile location data. In USA, the network operators are required to keep the data for at least a year. UK has a Voluntary Code of Practice on the retention of communications data since 2003 (updated in 2007 and 2009) that requires the data to kept for a year. In Australia, the Telecommunications (Interception and Access) Amendment (Data Retention) Act 2015 made it mandatory for network operators to retain data for a minimum of two years3.
It is understandable that mobile call data is not one of the first evidence lawyers consider in their preparation, given that there is other more significant evidence that needs to be considered first. However, lawyers invariably do not consider the mobile call location data at all or by the time lawyers consider accessing the information, the information is already lost. Therefore, it is best to request the data and figure out whether it is useful or not later.
Key uses of mobile location data
Mobile call location data is unlikely to give the exact location like GPS. While mobile call location data does not have the accuracy of GPS, it has the advantage of being more readily accessible and usually in large numbers. The USA examples discussed later in this article show that the law enforcement getting access to large amount of mobile phone location data was crucial in getting successful conviction.
Corroborate or destroy alibis
The first two cased are from USA, where mobile location data provided the crucial link to the suspect.
Rebecca Cleland was accused of hiring her two cousins to kill her husband. One of the key breaks was provided when the prosecution was able to prove that Cleland’s cousin Alvaro Quezada was lying. Cell phone data placed Alvaro Quezada about a block from the murder scene, despite his claim that he was at a restaurant 20 miles away1. All three were successfully convicted.
In 2005 Alejandro Avila was convicted for the murder of 5-year-old Samantha Runnion. Avila claimed that he was at an Ontario mall when the murder happened, however, his cell phone data showed that that he was near where Samantha Runnion’s body was found4.
The third case is a New Zealand example. The data presented is not the actual information but representative of it. In 2014 John Smith was convicted of assault. In the 2014 court case both defense and prosecution lawyers agreed that the cell phone call data was not relevant to the case. The case was appealed in 2016 and the primary evidence presented was mobile call location data. The accuser claimed that she was at her house around 10.30am when the assault happened. Her cell phone data showed there was a call at 10.22:34. The call lasted 33 seconds.
Table 1: Call data of the accuser
|Time||Call Duration||Serving cell at the start of the call||Serving cell at the end of the call|
Cell site Shirely was serving the call at the beginning of the call and cell site Edgeware was serving the call at the end. Figure 1 shows the two cell sites that served the call, nearby cell site Warrington and the accuser’s house (The House).
Figure 1: The accusers house in relations to the cell sites that served the call
The analysis considered whether it is possible for a call to be handed over from Shirley cell site to Edgeware cell site when a person was in The House. Using mobile phone signal measurement data taken at The House and propagation and statistical analysis, it was concluded that when the call was carried by Edgeware cell site the accuser was not in The House. She was in the highlighted areas, placing her few kilometers from The House. The appeal was successful and a retrial was ordered. Police dropped the charges in light of “new evidence”.
Track suspects' movements
In 2002 Danielle van Dam disappeared from her San Diego home. Prosecutors used David Westerfield’s cell phone records to track his movements in the days after and place him where van Dam’s body was found. Westerfield was convicted of kidnapping and murdering the 7-year-old girl4.
In a New Zealand case (not actual data, but representative of what happened) the accused claimed that he was not at the scene of the incident and was getting dropped off at work in Christchurch city centre around the time of the incident (around 10am). Table 2 shows the call data.
Table 2: Phone records of the accused
|09:56:44||SMS||Bealey Ave West|
|10:11:21||SMS||South City Centre|
|10:11:33||SMS||South City Centre|
|10:11:48||SMS||South City Centre|
Figure 2: Cell sites that served the accused and the direction of movement
The sequence of the cell sites that served the accused show movement from Bealey Avenue West to Christchurch city centre. In this case the call data corroborated accused’s alibi.
Place a person in a location at a particular time
Aaron Graham and Eric Jordan from Baltimore were convicted for six armed robberies in 2010 and 2011. Investigators used their cell phone location data for more than seven months to link them to the crimes. There were no eyewitnesses tying Graham and Jordan to the robberies, so their prosecution hinged on the cell phone data5.
Investigators got access to Davis’s cellphone call records for 5,803 calls and 11,606 location data points, an average of around one location data point every five and a half minutes for 67 days. That allowed them to put him in the area of robberies and establish where he was during a crime spree in Florida in 2010 and 2011. He was convicted and sentenced to almost 162 years in prison6,7.
Despite its limitation in accuracy, cell phone location data in large numbers helped the prosecutors to successfully get a conviction even when there was limited other evidence.
In UK in the murder trial of Sean Mercer, police were able to use mobile call data to demonstrate association at key times and place individuals at specific locations. It also showed that the mobile phones of the key offenders were in the area some twenty minutes after the murder – helping to establish that Mercer and other convicted associates attended business premises in order to burn the gunman’s clothing and douse him in petrol to remove firearms discharge residue. Sean Mercer was convicted of murder and six others were convicted of lesser charges
New Zealand is behind countries like USA and UK in making use of location information contained in cell phone data. In these countries cell phone location data has a level of acceptance where it is widely used to corroborate or challenge other evidence. In number of court cases cell phone call data played a key role in successful prosecution.
New Zealand laws do not require the retention of cell phone location data. Therefore, it is best to request the data early to avoid loss of crucial evidence.