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I am curious about a comment made in evidence at the London Bridge terror attacks inquest by the lawyer representing several of the victims' families:

There were "opportunities galore" to identify that the London Bridge extremists were plotting an attack, an inquest has heard.

(...)

Mr Patterson [said] that there was one occasion in May when all three men were at the gym "in the dead of night" and were speaking together in the street, but employed a "classic anti-surveillance technique" of leaving a telephone on the ground while they walked away and talked.

(Source1, emphasis mine)

From the transcript of the day's evidence (PDF):

Q. Well, they wouldn’t detach - - they wouldn’t stop thinking . They would be thinking to themselves: goodness me, that’s interesting , I wonder what’s going on, wouldn’t they?

A. A surveillance officer records all movements of the individual , sir .

Q. The person to whom he reports it back would be thinking goodness me, that’s interesting ?

A. Potentially , sir , yes.

Q. Yes, especially when the telephone is placed on the ground before the walk and talk begins, a classic anti - surveillance technique, isn’t it ?

A. Yes, sir

(LBI, Day 18, page 7 (PDF). Q - Mr Patterson, A - Acting Det Ch Insp Wayne Jolley. Emphasis mine.)

Some further context is given in the question and answer immediately following this:

Q. And again and again in these sorts of jihadist plots we see that they go to the centre of a boating lake or the centre of a park or an area of open land and walk and talk so they can distance themselves from any suspected microphones or surveillance techniques; that’s right , isn’t it ?

A. There are many different methods, sir

(ibid.)

I am curious as to how leaving a telephone on the ground in the street is considered an "classic anti-surveillance technique". What surveillance is this countering?

A phone tap - intercepting telephone communications - would not catch people talking in person. I don't believe that it would defeat correlation of locations either, as the individuals were still present at the same location and (from the description) presumably observed together.

What surveillance does leaving a telephone on the ground while walking away counter?

1: The transcript of the day's evidence was not available at time of writing

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bertieb
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    Feedback welcome! Also, I [posted on Meta querying if this is on-topic](https://security.meta.stackexchange.com/questions/3206/are-questions-on-law-enforcement-surveillance-techniques-on-topic) and was advised just to ask. – bertieb May 31 '19 at 16:19
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    I don't think there's much more here than simply assuming that a phone could be used as a bug, and leaving it behind. Lawyers like to play this stuff up as if it's some kind of cloak and dagger stuff, rather than just obvious stuff you'd see on a TV show. If they'd actually been good at op-sec, they'd just have all left their phones at home rather than having the potential to all suddenly come together at the same place. Traffic analysis is often more revealing than audio bugs. – Steve Sether May 31 '19 at 16:38
  • It seems you are right! From the original reporting, it appeared that leaving the phone on the ground was a key thing in itself; whereas it is one action of potentially many that people can take to distance themselves from surveillance. It seems this was done as the phone itself may be a source of intelligence. Both answers address this aspect. – bertieb Jun 03 '19 at 08:52

2 Answers2

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What surveillance does leaving a telephone on the ground while walking away counter?

If the mobile phone is compromised and acting as a covert listening device, also known as a "bug". To walk away is so that conversations are too far to be properly heard.

Nobody needs to actually use the phone and make a call for such surveillance to happen, it is just a thing that sits there and collects every sound around it.

Examples

Remotely turning on cell phone microphones, from 2012:

a judge published a statement that the FBI's established practice of remotely turning on cell phone microphones to monitor conversations was indeed legal.

Source: What are prudent security precautions to take for business travel by people with access to sensitive info?

Even smartphone gyroscopes could be re-purposed into microphones:

When the researchers tested their gyroscope snooping trick's ability to pick up the numbers one through ten and the syllable "oh"—a simulation of what might be necessary to steal a credit card number, for instance—it could identify as many as 65 percent of digits spoken in the same room as the device by a single speaker.

Source: https://www.wired.com/2014/08/gyroscope-listening-hack/

Further examples: https://www.schneier.com/blog/archives/2006/12/remotely_eavesd_1.html

Other parts of your question

Without further clarifying details from the lawyer, most likely:

I am curious as to how leaving a telephone on the ground in the street

The ground and street are just due to where this occurred, not specific to understanding the walk-away approach.

is considered [a] "classic anti-surveillance technique".

The classic is an adjective to describe the anti-surveillance technique, that it "has been done since long ago", implying "everybody" "should already know this". Then the lawyer can say that it is "obvious". From there, how such "obvious" things were missed, so that along with satisfying other requirements, the lawyer can establish that there was negligence and win the case.

clarity123
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Leaving it on the ground is irrelevant. Leaving it is the important bit.

As mobile phones can be subverted to act as microphones, leaving them behind when discussing sensitive topics is a way to be sure they have not recorded or transmitted your conversation. Actions like this, or taking in very loud environments etc, have been used by spies and criminals for years.

Rory Alsop
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