Detective Constable Tom Norrish, of the Major Crime Investigation Team, told the court that he believes the man in the baseball cap, who was first spotted outside the James Owen Court building in Sidwell St at 4.55am on August 7, was Kostov.
According to Devon Live, he said: 'We were aware that Tesco Express was just opening and putting the bins out.
"It is apparent he stops and rests throughout the whole journey. He is waiting for people to leave the area, and is resting and tired, in our opinion."
The CCTV subsequently shows him walking past a KFC, the Duke of York pub and Exeter mosque before the final sighting in Pennsylvania Rd just after 5am.
Norrish added there was no CCTV of anyone disposing of a body, but there was later footage of the same man walking on Pennsylvania Rd at 5.30am.
The case has already heard two weeks of the prosecution's evidence.
During the opening of the trial on April 20, Simon Laws, QC, prosecuting, said the couple had been in a relationship for 15 years prior to Prodanova moving to Exeter, Devon, in December 2015.
He said: "It was a complex and very troubling relationship. He had used physical violence against her on a number of occasions.
"He was a jealous and controlling man. He would lose his temper, especially when he had had a drink, and he would hit her.
"She stuck with him for many years. She seems to have found it very hard to break free from him."
The jury heard Prodanova moved to England on her own, leaving Kostov and her children at home in Bulgaria and soon formed a relationship with another man, who Laws said treated her "kindly" and made her happy.
Laws said Kostov flew to the UK on April 21, 2016 and moved in with Prodanova in a small flat on Mount Pleasant Rd in the city.
He said the prosecution case was that she was killed there on the evening of August 4 by Kostov because he was jealous of her new relationship.
"On August 4 last year Gergana Prodanova disappeared in Exeter," said Laws.
"She had not been in this country very long but she had made a small circle of friends and she had started a relationship with a man called Tihomir Todorov.
"She had a job and she was a dependable employee, so her new friends and her colleagues were surprised at her disappearance.
"Then messages were sent by text and Facebook that looked as if they came from her.
"Those messages were intended to explain her sudden absence.
"Nearly a fortnight later her body was found here in Exeter. It was concealed in a suitcase by the side of the railway not far from the prison.
"She had not disappeared at all. She had been killed by the defendant."
Laws also said Prodanova had her clothes cut up with scissors by Kostov after a row in May, three months before she was killed.
When her body was recovered near the rail line next to Exeter prison, it was found her clothes had again been cut up.
He said: "Whoever killed Gergana also cut up her clothing - clothing that she was wearing when she died - with a pair of scissors.
"Police found that clothing he had tried to dispose of. It would seem unlikely that anyone would be so unfortunate to have their clothing cut in that way by two different people in the space of three months."
Laws said Kostov told police Prodanova was alive the last time he saw her, that she had received a phone call from her sister to say that her mother was dead and had left the flat.
The prosecution has also claimed that Kostov searched 'How long would it take for a human corpse to decompose?' on the internet.
Laws said: "The defendant denies using his phone to deliberately search for information on the decomposition of the human body.
He will say that he was concerned that Gergana Prodanova had been given drugs by Tihomir Todorov and was searching for information on how long drugs would remain detectable in the human body.
"The defendant will say that he typed in his phone 'How long does it take to decompose in the human body?'"
The defence argued there was a mistranslated, but Katya Ford, a linguistic expert who translated the search, said she was surprised by this claim.
She told the court: "There is no mention of drugs or a word that could be interpreted as possibly being drugs," she said.
Laws responded: "What about 'in the human body"? - Laws.
Ford added: "This is wrong. The word 'in' is not in that search box," she said. "There is an emphasis on corpse. The word used is for a dead body. It is the last word in the sentence."
The trial continues.
