Police fabricated evidence to incriminate five Americans facing trial in Pakistan on terror charges, lawyers representing the men will argue in court this week.

The men, all Muslims, were arrested in December in the central town of Sargodha, and have been charged with planning terrorist acts in Pakistan, Afghanistan and the US.

While the men admit wanting to travel to Afghanistan, they deny involvement in any jihadist activities and say they were planning to carry out "community work" in the country.

Defence lawyers will argue the men could not have made email contact with a Pakistani extremist linked to al-Qaida in the way the police claim.

According to the police's own summary of the investigation submitted to the court, investigators discovered the email account which was allegedly used to make contact several days after police had briefed journalists on the messages.

Similarly, the police report describes the discovery of maps of alleged target sites and other incriminating evidence more than two weeks after they had already told media about their existence.

The defence will also call into question police claims about the date of the men's arrest, which is several days after their widely reported detention on 9 December last year. Umer Farooq, 24, Waqar Hussain Khan, 22, Ramy Zamzam, 22, Ahmed Minni, 20, and Aman Hassan Yemer, 18, were charged under anti-terrorism laws.

Police say the group's intended target was Chashma Barrage, a complex located near nuclear power facilities in Punjab that includes a water reservoir and other structures.

The men, who pleaded not guilty, face life sentences if convicted on the most serious of the charges. They all grew up in the suburbs of Washington DC, where they were a tight-knit, religious group of friends. The Farooqs are originally from Sargodha and the men claim they had travelled to the Pakistani town to attend Umer's arranged marriage.

According to the police, the men were taken into custody on 9 December, but were allowed to go home each evening, and were only formally arrested five days later on 14 December. But there are no reported sightings of the men after 9 December.

Farooq's father Khalid, who was held for nearly three weeks before he was released, said that all of them were in continuous police custody after 8 December. "I was with the boys, in the same cell," he said. "There's no question of them being allowed out."

His son, Umer Farooq, 24, is on trial with Waqar Hussain Khan, 22, Ramy Zamzam, 22, Ahmed Minni, 20, and Aman Hassan Yemer, aged just 18. All of them grew up in the suburbs of Washington DC, where they were a tight-knit, religious, group of friends. The Farooqs are originally from Sargodha and the men claim they had travelled to the Pakistani town to attend Umer's arranged marriage to a local woman.

In a letter to Zamzam's parents seen by the Guardian, the men, who allege they were beaten by police and deprived of sleep and food in custody, face life in prison if convicted on the most serious of the charges.Following the arrest of the men, on 10 and 11 December police gave on-the-record briefings to local and international media about a Yahoo email account used to communicate with a Pakistani extremist called Saifullah.

They also said at the time that maps and jihadi literature were found with the men. But according to the police report lodged with the anti-terrorism court in Sargodha, where the men are being tried, it was only on 17 December that the suspects disclosed "their secret email address along with password" – allowing the investigators to find the communication with Saifullah.

In the document, a copy of which was seen by the Guardian, the police say that they found the extremist literature and maps on 26 December.

Defence lawyer Hasan Dastagir alleges that police misrepresented the date of the men's arrest in order to allow for inconsistencies in the evidence.

"By the ninth, the police had made up their mind what they were going to plant on these boys, because they had nothing on them," said defence lawyer Hasan Dastagir Katchela. "There are going to be some massive surprises (in court)."

The trial of the men resumes this on Saturday, 17 April.

According to Katchela, the later time given for the arrest was to allow police to create emails and other evidence dated after 9 December, and police have had to change the dates for the discovery of evidence, to fit the timing when they were "cooked up".

As they were transported to a court hearing in early February, the men tossed a note to journalists scribbled on toilet paper, alleging that they had been tortured.

The claims were repeated in a letter from Zamzam which was passed to his parents in March by US state department officials.

In the letter, seen by the Guardian, he wrote: "We were taken to a place where I still don't know where it was (we were blindfolded) and there were like 30 police and [intelligence] agency people who beat and tortured us. We were not given food or water for I counted to be at least 36 hours and they wouldn't let me sleep. ... They told us not to say anything to anyone about what happened … [unreadable word] they even threatened to electrocute us the day before court so we don't tell the judge but we spoke out and we did the toilet paper [note] so the world could know."

Usman Anwar, the district police chief for Sargodha, said the emails were genuine and "clearly show their evil intentions". He also denied the allegations of abuse, adding that the men had been "advised by their lawyer to make a hue and cry" to gain public sympathy.

The trial of the men resumes on Saturday.