Pakistan's police are on the front line battling the Taliban. Not just in the remote north of the country, near the border with Afghanistan, but in Karachi, the country's economic and cultural heart.

Five months ago the Taliban staged an audacious attack. Ten heavily armed men dressed as security guards stormed the cargo terminal of Pakistan's busiest airport, in Karachi, aiming to hijack aircraft. In a prolonged overnight battle most of the militants were shot and the rest blew themselves up. Altogether, at least 28 people died.

Karachi Police are fighting back against the Taliban by trying to root out militants hiding in the city suburbs, but it's dangerous work. Out of 15,000 police officers in the city, on average one dies every day.

"They are not pious. They are common criminals," says Ijaz, a senior officer in Karachi Police Criminal Investigation Department.

"They generate money from drug sales, extortion and kidnap to fund their war. Any crime you can think of the Taliban is involved in. You will find them in gambling dens, with liquor bottles and they often use the services of prostitutes."

Ijaz is in his early 30s but he has the look of much older man. When I walk into his office, he's enveloped in a cloud of thick smoke. He always seems to have a phone in one hand and a cigarette in the other.

"It's easy to fight them in the north of Pakistan because there is a clear target," he says. "But in a city like Karachi it's very difficult because there are more than 70 splinter groups… and you don't know who your enemy is. We are in a real war."

Image copyright AFP Image caption There were reports of at least two huge blasts during Jinnah International Airport attack in June

Image copyright AFP Image caption Fire fighters at the smouldering cold-storage facility after the attack on the airport

For more than a decade Pakistan's economic capital has been plagued by politically motivated targeted killings but now all the parties have a common enemy in the Taliban, who turn its ethnic diversity to their advantage.

"They hide in the slums where no one raises an eyebrow if you are Pathan or Punjabi or from the tribal areas," Ijaz says. "You can come from any part of Asia and no one will look at you twice. You can go completely undetected."

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Ijaz and his team of 25 heavily armed officers carry out regular night raids in some of these hiding places, which have fast become no-go areas for other police units, especially after sunset.

I ask if I can accompany them and I'm told to be patient. Then suddenly one night after dinner my phone beeps. The message reads: "Raid tonight - I'll pick you up at 23:45. I have bullet proofs for you."

When we set off Ijaz explains that we're on our way to the house of a suspected handler of suicide bombers. Police believe he is responsible for taking them to the places where they blow themselves up.

Soon the bright lights of central Karachi are far behind us. We drive past buildings which look like empty shells and I can see swirls of dust in our headlights. Ijaz tells me his force often carries out multiple raids between 1am and 4am in crowded, run-down neighbourhoods. In some, locals have to pay protection money to the Taliban and outsiders can't move around freely.

"There are hideouts, there are sympathisers and there might be weapons so we need to be careful," says Ijaz.

Image copyright AFP Image caption The wreckage after a car bomb attack targeting a senior police officer in Karachi in September

But as our cavalcade of five vehicles bumps off the main road and drives noisily down a dirt track I can't help thinking that our approach is anything but discreet.

Ijaz explains that when we arrive, some officers will use ladders to go up the walls of the two-storey house, while others search the premises. "In the meantime our drivers will be turning around our vehicles so we don't have to wait for even a few seconds. When we arrest someone we get out of the area as fast as possible."

Eventually the car screeches to a halt and Ijaz puts on a mask. Police are routinely targeted by Taliban-affiliated groups.

A couple of officers shine torch lights into the courtyard to see if there's anyone awake. A policeman with a gun is climbing over the fence while another hammers on the door.

Moments later a sleepy looking man in a vest is brought out of the house. Police ask him his father's name then bundle him into the car and drive back to the station.

Policing Karachi

Image copyright AFP

The police in Karachi are stretched, with 15,000 active officers in a city of more than 20 million people

On average, one police officer a day is killed on duty

The judicial process is very slow - in the 12 months since September 2013, police in Karachi have filed 322 terrorism cases and 115 cases of kidnap for ransom but none of these have come to trial yet

In Ijaz's heavily armed compound, there are always suspected Taliban members being held for questioning. He is open about the use of what he calls "arm twisting". He admits waterboarding is sometimes used, and I spot a taser gun in his hand although I do not witness him using it.

"You can't present a suspect with a bouquet and ask him to tell the truth," he argues. "You can't say, 'I'll give you a Snickers bar if you tell me the truth,' because they are not kids, they are hardened criminals and they need to be treated like this."

The Human Rights Commission of Pakistan, however, takes a different view. It has accused the Karachi police of torturing people in custody and even carrying out extrajudicial executions.

I am not permitted to speak to the man police have just picked up but Ijaz does later allow me to speak to another Taliban suspect.

The man brought in has sweat dripping down his neck, but he's not nervous - in fact he tells me he wants to talk. He's wearing handcuffs, and a blindfold designed to keep me and the police safe from reprisals.

It's impossible to know how honestly he will answer my questions, especially as Ijaz is standing over him in the windowless interrogation room wielding a cane.

But he seems eager to tell me what he's done.

"I prepare boys for suicide missions. We get teenagers, 13 or 17 years old. We give them passion for violent jihad and tell them they should sacrifice themselves for their religion," he says.

"I've planted bombs in this city. I can put a bomb in a car, a rickshaw or a cement block. I've killed 20 or maybe 25 people in these attacks. When I see the news about people dying, it makes me happy because these people are hypocrites. I can use guns too. I've killed four or five policemen too. I use a 9mm pistol."

Image caption Police officers in Karachi attending the funeral of one of their colleagues

The prisoner is chillingly clear when it comes to his motivation for carrying out such attacks. "These people are partners of America. They are all hypocrites. The police, the army, they are all partners of America."

When I point out that murder, extortion and selling drugs are all explicitly un-Islamic, he retorts: "We have to pay for guns and bullets. Do you think these things are free? Our leader has said these things are OK because we are at war. We are fighting a holy war."

It's impossible to know whether he is speaking honestly or if he sees our conversation as an opportunity for Taliban propaganda.

Later, I hear that he has been charged with murder and conspiring against the state. When his case will come to court is hard to predict, but it's unlikely to be soon as Pakistan's judicial system is notoriously slow.

In the 12 months from the start of September 2013 to the end of August this year not a single terrorism case resulted in a conviction.

Ijaz says this has a demoralising effect on his colleagues.

"Witnesses are fearful for their lives. Testifying in court against the Taliban is a risk that many people are just not willing to take," he says. "We also have a real lack of resources in terms of phone-tapping and forensic evidence. It can often take 10 years or more for a case to go through the courts. Justice delayed can often be justice denied."

But Ijaz himself remains motivated.

"We will not be bullied by these terrorists," he says. "That is the moral victory. We will gain physical victory one day, inshallah."

Listen to Mobeen Azhar's report on Crossing Continents on BBC Radio 4 on Thursday 20 November at 11:00 GMT - or find it soon after on BBC iPlayer

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