Police following Jean Charles de Menezes may have suspected he was using counter-surveillance techniques before he was shot dead, a court has heard.
The Brazilian, wrongly suspected as a suicide bomber, left a bus and then got back on minutes before being killed in a London Tube station on 22 July 2005.
Counsel for the Met Police told the Old Bailey surveillance teams could regard those movements as a criminal tactic.
The force denies breaking health and safety laws over the shooting.
Mr de Menezes died the day after the failed 21 July 2005 suicide bombings.
The Met says that while Mr de Menezes's death was a tragic mistake, it was not a crime because officers thought they were dealing with a suicide bomber.
Ivor, an undercover officer who held Mr de Menezes as he was shot in the head, told the court how he had earlier seen the Brazilian get off a bus in Brixton town centre - and then very quickly rejoin it.
Mr de Menezes had got off the bus and began walking towards the Brixton Underground Station - but after 20 metres turned back when he saw the station was temporarily closed.
Ivor had been on the same bus watching the target - but did not rejoin it out of fear of compromising the surveillance.
However, he reported Mr de Menezes's movements on his radio, but had not seen the Tube station was closed.
Ronald Thwaites QC, defending, told the court that given the officers did not know Brixton station was closed, it would have been "obvious" to suspect the suspect was using counter-surveillance tactics to lose a tail.
"All I can reaffirm is what I saw and what I transmitted on my radio," said Ivor, denying that he had made such a suggestion to colleagues or Scotland Yard commanders. "It may have had any number of innocent explanations."
"If people deploy anti-surveillance methods it's usually because they are up to no good, isn't it?" asked Mr Thwaites.
"Criminals employ anti-surveillance techniques," said Ivor.
"And you were feeding back what you saw, knowing that people hearing these things would draw their own conclusions."
"I was simply transmitting what I saw. I can't comment on the mindset of other officers who were monitoring my communications," replied the policeman.
On the first day of his evidence, Ivor had told the court how he acted to restrain Mr de Menezes in the Tube carriage after seeing armed officers rush onto the platform.
In the confusion, firearms officers dragged Ivor out of the train and levelled guns against his chest and head.
He was dressed almost identically to the suspect and carrying a rucksack.
The case continues.