The US Department of Justice has launched an investigation into revelations that the Drug Enforcement Agency uses surveillance tactics – including wiretapping and massive databases of telephone records – to arrest Americans, amid growing concerns from lawyers and civil rights groups over its lack of transparency.

Reuters on Monday detailed how the Special Operative Division – a unit within the DEA comprising representatives of two dozen agencies including the FBI, CIA, NSA, Internal Revenue Service and the Department of Homeland Security – passes tips from wiretaps, informants and a database of telephone records to field agents to investigate and arrest criminals. Reuters reports that, although such cases rarely involve national security issues, the DEA agents using the tips are trained to "recreate" the source of the criminal investigation to conceal its true origin from defence lawyers, prosecutors and judges.

The revelations, which follow the Guardian's recent disclosures of the National Security Agency's wholescale collection of US phone data, have raised concerns among judges, prosecutors and civil rights lawyers over a lack of transparency. Many said the SOD practice violates a defendant's constitutional right to a fair trial.

James Felman, vice-chair of criminal justice at the American Bar Association, said the DEA story "connects the dots" over the government's potential abuse of phone records collected by the NSA.

Felman, an attorney in Tampa, said: "By the sound of it, this is a routine practice of using masses of information on Americans, in an erosion of constitutional protections of our citizens. This is clear evidence of things that people have been saying they are not doing. Collecting data on ordinary citizens and then concealing it officially. It is indefensible."

"I don't think that most people would believe that our government would be using these measures and using this excuse when they want to investigate heavy offences," he said. "What is upsetting is that it appears to be policy and practice to consensually conceal information that should be disclosed."

While the NSA data collection is aimed at thwarting terrorists, the SOD programme is focused on criminals such as drug dealers and money launderers.

One former federal agent who received tips from the SOD described the process to Reuters. He told how he would instruct state police to find an excuse to stop a certain vehicle on which they had information, and then have drug dogs search it. After an arrest was made, agents would then pretend that the investigation began as a result of the traffic stop, and not because of the information the SOD had passed on.

A training document quoted by Reuters described the practice whereby agents would "recreate" the source of the investigation, as "parallel construction". A dozen current or former federal agents interviewed by Reuters confirmed they had relied on parallel construction.

Nancy Gertner, a Harvard Law School professor who served as a federal judge from 1994 to 2011, described the practice of "parallel construction" as "a fancy word for phonying up the course of the investigation". It was one thing, she said, to create special rules for national security, but creating rules for ordinary crime threatened to undermine the bill of rights, set up as a check against the power of the executive.

"The best way to describe it is the government is saying 'trust us'," said Gertner. "The bill of rights is clear that we don't."

Gertner said that defence attorneys had a right to know and examine the source of the information against their clients.

"Even if a judge approved a wiretap, it doesn't mean there wasn't exculpatory or tainted evidence," she said. "If the judge does not know the genesis of the information there cannot be judicial review. When the DEA is concealing what the source of the information is and pretending it came from one place rather than another, there can be no judicial review."

Gertner and other legal experts said that there was no need to conceal such information in court, as there are already procedures by which judges can examine sensitive information in private to determine whether it is relevant.

The implications for existing cases, Gertner said, were difficult to assess.

"There needs to be an investigation and disclosure about the extent to which this information was used in previous investigations."

Civil rights campaigners said the latest revelations about surveillance programmes were an indictment of how easily the NSA data collection can be abused.

Ezekiel Edwards, the director of the American Civil Liberties Union's criminal law reform project, said: "With the uncovering of this massive surveillance programme, the government are reassuring people that they are very selective, that they are not using it on ordinary citizens.

"The opposite case is one of our concerns.

"What you have here is the DEA tapping into the vast NSA spying programme and using it to launch criminal cases on Americans. Not in national security cases, but other cases."

Edwards said it was a case of "mission creep", after the shift in the balance between civil liberties and security that happened in the US in the aftermath of 9/11.

He said that the concealing of information about the source of an investigation was unconstitutional because it did not allow defendants their right to confront and examine the evidence the government has against them.

"Evidence can be flawed, people can lie, innocent people can be convicted," Edwards said. "The reason we have trials is to determine whether evidence is reliable, but if you don't know the source of that evidence – that email or that phone call, it is impossible to argue that it wasn't me on the phone or that person is an invalid witness."

In a statement, the NSA said: "If a law enforcement agency thinks they have a valid foreign intelligence requirement, they can pass that information to the [intelligence community], which treats it as they would any other nomination. NSA works closely with all intelligence community partners … This co-ordination frequently includes sanitising classified information so that it can be passed to personnel at lower clearance levels in order to meet their operational requirements."

The statement added: "If the intelligence community collects information pursuant to a valid foreign intelligence tasking that is recognised as being evidence of a crime, [it] can disseminate that information to law enforcement, as appropriate."

Henry Hockeimer, a former federal prosecutor, said: "For the system to work, criminal cases should be built with a high degree of transparency. Not built through covert means. To use this in cases not involving national security and in routine drug cases is troubling.

"Now it's getting into the realms of a law enforcement tool, which is not what the normal person would have any degree of tolerance for. What other cases could be potentially built in the dark?"

The Department of Justice confirmed it was looking into the revelations, but declined to provide details. In an email to the Guardian, a spokesman said they were "looking into the issues raised by this story. We'll decline to comment further at this time."

The SOD played a major role in a DEA sting in Thailand against Russian arms dealer Viktor Bout in 2008. He was sentenced in 2011 to 25 years in prison on charges of conspiring to sell weapons to the Colombian rebel group Farc.

The SOD also recently coordinated Project Synergy, a crackdown against manufacturers, wholesalers and retailers of synthetic designer drugs that spanned 35 states and resulted in 227 arrests.

• This story was updated on 7 August 2013 to include a statement from the National Security Agency.