ROME (Reuters) - The United States has denied suggestions it undermined an investigation into a massive data breach at the Italian cybersecurity firm Hacking Team, saying it did everything it could to help in the case. A Milan magistrate last week recommended shelving an investigation into six people who were suspected of orchestrating the 2015 data theft. A senior judicial source criticized U.S. officials for not handing over a computer belonging to a key suspect, saying it might have contained information vital to the probe.  But in a comment emailed to Reuters, the U.S. Department of Justice in Washington denied the United States was to blame for the case floundering.  The United States assisted Italy to the greatest extent possible and the relevant Italian authorities know that,  a U.S. Department of Justice spokesperson wrote. Magistrates opened their investigation in July 2015 after hackers downloaded 400 gigabytes of data from the firm, which makes software that allows law enforcement and intelligence agencies to tap into the phones and computers of suspects. Much of the data later showed up on the WikiLeaks website. The company said at the time it believed former employees had stolen vital code that gave them access to its systems. It also speculated that a foreign government might have been behind the hacking. The Italian probe led magistrates to a suspect living in Nashville, Tennessee. U.S. authorities raided his house and took the man in for questioning, however a senior judicial source in Milan, with direct knowledge of the case, said his computer was never sent to Italy for technical assessment.  We could not carry out the checks on the computer to see if it contained the evidence that we were looking for because the United States did not give it to us. We did not receive an explanation for this decision,  the source said. 