With one word, the young Romanian in the dock at Manchester crown court brought to a gratifyingly early end one of the 1,802 rape cases dealt with by Greater Manchester police (GMP) in the last year. “Vinovat,” said Bogdan Drezaliu, 21, when asked via his interpreter on Friday morning if he admitted attempting to rape a jogger in a north Manchester park. Guilty.

The early plea saved his victim the agony of reliving her ordeal in court. It was never going to be easy for Drezaliu to deny the offence: his semen was found on the back of his victim’s knickers.

He would have had difficulty claiming that the woman consented – she screamed so loudly when he pounced on her that a dog walker rushed to her aid. They kicked him until he escaped on his bike. He was caught nearby a week later after groping a teenage girl’s bottom in the street; her father went after him and performed a citizen’s arrest.

It wasn’t Drezaliu’s first offence. In 2012 he was convicted of a similar sexual assault involving a prostitute in Manchester. He wasn’t jailed then. But in court on Friday his lawyer, Hunter Gray, accepted that a custodial sentence was inevitable this time. Drezaliu will be sentenced on 26 June. The groping charge, along with another of indecent exposure, will lie on his file.

At home on the other side of Manchester, DC Janet Malone celebrated. She wasn’t supposed to be working until 5pm but immediately tried to phone the victim and tell her the positive news.

It had been a good week. On Thursday another big case ended with a conviction. Hamid Zaman, 35, was sentenced to 12 years in prison after being found guilty of orally raping and beating a woman at Boggart Hole Clough in New Moston, north Manchester, on Halloween last year. After raping and repeatedly punching and kicking her in the head, he struck her across the head with a brick and a glass bottle.

Police arrived as Zaman was attacking the woman and he was tasered before being arrested. Still he maintained his innocence. A jury didn’t believe him.

Malone is one of 60 officers working in GMP’s serious sexual offences unit (SSOU), which is profiled in a BBC2 three-part documentary starting this Sunday. Based in a heavily fortified modern building in Ashton-under-Lyne, the officers spend all of their time investigating rape or attempted rape. “You have to be a people person, rather than a cold, hard facts person, like some detectives are,” said Det Supt Jon Chadwick, who has run the SSOU since its inception three years ago.

“Rape victims are a class of people on their own … It just has an impact like no other crime. Trying to keep that person safe, manage their expectations day to day, trying to get them into the recovery process – that’s the biggest challenge.”

Det Supt Jonathan Chadwick at Greater Manchester Police ( GMP) serious sexual offences unit. Photograph: The Guardian/Christopher Thomond

That’s why Chadwick decided to set up the SSOU. “It was about getting a bit wiser to the fact that rape is a special crime. We’ve had murder teams, drug teams, armed robbery teams for ages. This was about realising we should be doing a lot better and doing things differently, because rape has such a massive impact on victims. The idea is you can teach anyone to be a detective. You can’t teach anyone to be a good rape detective, because it’s about the way they deal with victims.”

In the three years the unit has been running, two rape survivors killed themselves after GMP and the Crown Prosecution Service (CPS) took their abusers to court. In January 2013 Frances Andrade committed suicide after giving evidence against her abuser, Michael Brewer, former head of music at Chetham’s school of music in Manchester. The following February a woman called Tracey Shelvey threw herself off a car park roof in Rochdale after the man she and five others accused of rape was acquitted. Occasionally suspects take their own lives too, sometimes leaving notes protesting their innocence.

When a person has been raped, they’re “all over the place”, said Chadwick, a laconic man with a goatee beard and idiosyncratic fashion taste.

Rape victims are a class of people on their own … It just has an impact like no other crime Det Supt Jon Chadwick

Rape detectives have to accept that the first account given by a victim may have holes in it, he said. “It will be inaccurate, it could be at the wrong time, the wrong day, the wrong place, in the wrong order. And there is an instinct among detectives that you just want to check things straight away.



“But the fact is, if someone has just been raped they will get things wrong. You need the right person listening and taking that case from the start and building around the victim, rather than thinking, ‘hang on, that’s not what she said, she’s got the day wrong.’ All the investigative skills are there. You just have to have a more open mind.”

From the start, Chadwick knew his officers would be busy. But he was not prepared for how overwhelmed the unit would be. In 2011-12, GMP recorded 737 rapes. Three years on, that figure had leapt 124% to 1,649 – a result, he thinks, of increased public confidence in the police. Around 40% of these reports are domestic incidents. The same percentage of the total are classed as “historic” because they weren’t reported until a year or more after the attack.

The conviction rate for rape in Greater Manchester, however, is poor. According to the CPS, in 2013-14, 274 cases reached court, with just 158 ending with successful prosecutions. That can be explained by GMP charging more rapes than other areas, argued Chadwick. “You go to other CPS areas and you need the most airtight case you’ve ever seen in your life before the CPS will charge it, and then you get a high conviction rate because you only send rock solid cases to court.”

Whether running a trial which the prosecution might lose is good for the victim is another question, he said. “That’s a case-by-case thing. I don’t think you can generalise.”

The unit must keep up as the law changes. Last month GMP received two complaints of revenge porn within days of new legislation coming into force making it a criminal act to disclose private sexual photos with intent to cause distress. On Friday the first man to be charged under the act in the area appeared by video link at Bolton crown court. Kevin Bond, 30, is accused of raping a woman twice in her home and then sending intimate images of her to another person.

Modern technology offers ever more opportunities for the determined rapist, said Chadwick. “We’re seeing an increasing number of people being raped by people they meet on dating sites. It’s just another tool that’s easy for rapists. You don’t have to approach someone in a bar any more. You can do it all online and rape them on the first meeting.”

A whiteboard in the Ashton office keeps track of how many live cases the unit is juggling. On Wednesday it was 272. They were looking for just 12 suspects: the board said three were believed to be in Pakistan; another in South Africa. The unit works in shifts from 7am to 11pm, seven days a week. The Sunday morning shift is known by officers as “rape o’clock”, when officers are deluged with reports of alcohol-fuelled crimes from the previous night.

In a windowless office where they used to keep the photocopier, DCI Colin Larkin was having a difficult phone conversation. A rape victim with mental health problems was haranguing him over the lack of progress in her case. “She wants answers and the answers are not always forthcoming,” he said with a sigh.

DCI Colin Larkin at Greater Manchester police serious sexual offences unit. Photograph: The Guardian/Christopher Thomond

Rape investigations have changed a lot since Larkin joined the force 25 years ago. “A victim used to ring up and say, ‘I’ve been raped’. Previously, before we made a crime report, we would try and prove or disprove – in some cases, not believing the victim. Now we always believe the victim in the first instance. Sometimes, when investigating, we can prove that the victim has lied or misunderstood or whatever. But we start off by believing them.”

Around the corner, a detective was investigating a crime which from the outset looked unlikely to ever reach court. A 14-year-old girl in Bolton, already known to police as being at high risk of child sexual exploitation (CSE), had accused an older man of raping her while her friend went off and had consensual sex with another man.

The officers who attended the scene quickly encountered a problem: her friend insisted it was all lies and that the pair had stuck together all evening. Looking through the alleged victim’s file on the police computer, it emerged that this is not the first time she has made an allegation of rape. But an officer must still dedicate time to the case, in consultation with a dedicated CSE unit.

The new victim-focused approach can be “massively frustrating” when officers know people are wasting their time by making false reports, admitted Larkin: “We do get people making up allegations because they want to get their own back, for whatever reason. If A and B are courting and A has an affair with C, sometimes B will say that A has raped her … It’s not massively common but it isn’t uncommon either.”

Later, Larkin’s boss, Chadwick, explained that less than 3% of all rape reports received by GMP turn out to be fabricated. But unlike other forces, GMP has never prosecuted a victim for making a false allegation. Instead, they have dished out the odd fixed-penalty fine for wasting police time. “The numbers are very low,” said Chadwick. “One of the considerations is the vulnerability of the victim. Generally those people making false reports have some sort of vulnerability.”

Chadwick adds: “Murder is easy compared with dealing with this. And I’ve done a lot of murder. It’s a completely different game when you’ve got a human being who has been subject to the worst crime you can be subjected to and survive.”

The Detectives starts on BBC2 on Sunday at 9pm.